Focus adjustment device, imaging device and focus adjustment method

ABSTRACT

A focus adjustment device includes an image sensor that includes imaging pixels for capturing an image formed via an imaging optical system and focus detection pixels for detecting a focus adjustment state at the imaging optical system through a first pupil division-type image shift detection method, a focus detector that detects a focus adjustment state at the imaging optical system through a second pupil division-type image shift detection method different from the first pupil division-type image shift detection method, and a focus adjustment controller that executes focus adjustment for the imaging optical system based upon the focus adjustment states detected by the image sensor and the focus detector.

INCORPORATION BY REFERENCE

The disclosures of the following priority applications are hereinincorporated by reference:

-   Japanese Patent Application No. 2006-54491 filed Mar. 1, 2006-   Japanese Patent Application No. 2006-54492 filed Mar. 1, 2006

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a device that adjusts the focus of animaging optical system, an imaging device equipped with the focusadjustment device and a focus adjustment method.

2. Description of the Related Art

There is a digital camera known in the related art (see Japanese LaidOpen Patent Publication No. 2001-281530) that includes a focus detectionsensor adopting a phase difference detection method and an image sensor.This digital camera first drives the imaging optical system to a pointnear the focus match position based upon the results of detectionexecuted by the focus detection sensor, then detects the focus matchposition through a contrast detection method by using the output fromthe image sensor and executes fine adjustment to the focus matchposition.

However, the contrast detection method and the phase differencedetection method adopted in the camera in the related art describedabove are not perfectly compatible with each other since their focusdetection principles are different and, for this reason, thecorrespondence of the focus detection results obtained through the twomethods tends to be poor. For instance, there may be a photographicsubject for which the focus can be detected successfully through thephase difference detection method but the focus detection cannot beexecuted successfully through the contrast detection method. Inaddition, while the focus may be detected with a high level of accuracythrough the phase difference detection method for a given photographicsubject, the accuracy of the focus detection for the same photographicsubject executed through the contrast detection method may be poor.Under such circumstances, the imaging optical system may hunt for, andfail to reach the focus match point, the imaging optical system may bedriven to an unexpected position or the imaging optical system may notmove at all when the camera attempts to fine-adjust the position of theimaging optical system through the contrast detection method afterdriving the lens to a point near the focus match position through thephase difference detection method.

SUMMARY OF THE INVENTION

According to the 1st aspect of the invention, a focus adjustment devicecomprises an image sensor that includes imaging pixels for capturing animage formed via an imaging optical system and focus detection pixelsfor detecting a focus adjustment state at the imaging optical systemthrough a first pupil division-type image shift detection method, afocus detector that detects a focus adjustment state at the imagingoptical system through a second pupil division-type image shiftdetection method different from the first pupil division-type imageshift detection method, and a focus adjustment controller that executesfocus adjustment for the imaging optical system based upon the focusadjustment states detected by the image sensor and the focus detector.

According to the 2nd aspect of the invention, a focus adjustment devicecomprises an image sensor that includes imaging pixels for capturing animage formed via an imaging optical system and focus detection pixelsfor detecting a focus adjustment state at the imaging optical systemthrough a first processing process, a focus detector that detects afocus adjustment state at the imaging optical system through a secondprocessing process different from the first processing process, and afocus adjustment controller that executes focus adjustment for theimaging optical system based upon the focus adjustment states detectedby the image sensor and the focus detector.

The focus adjustment device may further comprise an optical elementcapable of directing a light flux from the imaging optical system alonga light path extending toward the image sensor and along a light pathextending toward the focus detector.

The image sensor may include the imaging pixels and the focus detectionpixels disposed on a single substrate.

The focus detection pixels may each include a micro-lens and a pair ofphotoelectric conversion units provided in correspondence to themicro-lens.

The focus detector may include a pair of re-focusing lenses forreforming an image formed at a predetermined image plane of the imagingoptical system and an image sensor that detects images reformed via thepair of re-focusing lenses.

A range of focus adjustment state detection achieved through the secondimage shift detection method may be greater than a range of focusadjustment state detection achieved through the first image shiftdetection method.

A range of focus adjustment state detection achieved through the secondprocessing process may be greater than a range of focus adjustment statedetection achieved through the first processing process.

A threshold value used in the second image shift detection method as towhether or not a detection of the focus adjustment state is possible maybe greater than a threshold value used in the first image shiftdetection method as to whether or not detection of the focus adjustmentstate is possible.

A threshold value used in the second processing process as to whether ornot a detection of the focus adjustment state is possible may be greaterthan a threshold value used in the first processing process as towhether or not detection of the focus adjustment state is possible.

According to the 4th aspect of the invention, a focus adjustment devicecomprises an image sensor that includes imaging pixels for capturing animage formed via an imaging optical system and focus detection pixelsfor detecting a focus adjustment state at the imaging optical system, afocus detector that detects a focus adjustment state at the imagingoptical system, and a focus adjustment controller that executes focusadjustment for the imaging optical system based upon the focusadjustment states detected by the image sensor and the focus detector.The focus adjustment controller executes focus adjustment based upon thefocus adjustment state detected by the focus detector when the focusadjustment state indicates a value greater than a predetermined valueand executes focus adjustment based upon the focus adjustment statedetected by the image sensor when the focus adjustment state indicates avalue smaller than the predetermined value.

According to the 5th aspect of the invention, a focus adjustment devicecomprises an image sensor that includes imaging pixels for capturing animage formed via an imaging optical system and focus detection pixelsfor detecting a focus adjustment state at the imaging optical system, afocus detector that detects a focus adjustment state at the imagingoptical system, and a focus adjustment controller that executes focusadjustment for the imaging optical system based upon the focusadjustment states detected by the image sensor and the focus detector. Arange over which the focus adjustment state detected by the focusdetector is judged to be in focus is wider than a range over which thefocus adjustment state detected by the image sensor is judged to be infocus.

The focus adjustment device may further comprise an imaging controllerthat controls a start and an end of an imaging operation executed tocapture an image obtained via the image sensor.

The focus adjustment controller may execute focus adjustment for theimaging optical system based upon the focus adjustment state detected bythe focus detector until the imaging operation is started by the imagingcontroller, and execute focus adjustment for the imaging optical systembased upon the focus adjustment state detected by the image sensor oncethe imaging operation starts.

According to the 6th aspect of the invention, a focus adjustment devicecomprises an image sensor that includes imaging pixels for capturing animage formed via an imaging optical system and focus detection pixelsfor detecting a defocus amount indicating an extent of defocusingmanifesting at the imaging optical system through a pupil division-typemethod, a focus detector that detects a focus adjustment state at theimaging optical system through a pupil division-type method, a focusadjustment controller that executes focus adjustment for the imagingoptical system based upon the focus adjustment states detected by theimage sensor and the focus detector, and a corrector that corrects thedefocus amount detected by the focus detector by adding an offsetthereto so as to equalize the defocus amount with the defocus amountdetected by the image sensor.

The offset may represent a difference between the defocus amountdetected by the image sensor and the defocus amount detected by thefocus detector in correspondence to a single photographic subject.

The offset can be set in correspondence to optical characteristics ofthe imaging optical system, and can be set in correspondence to aminimum f-number of the imaging optical system.

The focus adjustment device may further comprise a storage device thatstores the offset. In this case, the focus adjustment controller canupdate the offset based upon the defocus quantities detected by theimage sensor and the focus detector.

The image sensor and the focus detector may each detect the defocusamount over a plurality of focus detection areas corresponding to aplurality of positions set on an estimated focus plane of the imagingoptical system. The focus detection controller can select one of thefocus detection areas based upon the defocus amount detected by thefocus detector and execute focus adjustment for the imaging opticalsystem based upon the defocus amount detected by the image sensor incorrespondence to the selected focus detection area.

According to the 7th aspect of the invention, an imaging devicecomprises an image sensor that includes imaging pixels for capturing animage formed via an imaging optical system and focus detection pixelsfor detecting a focus adjustment state at the imaging optical systembased upon a shift amount between a pair of images formed with lightfluxes passing through a pair of areas on a pupil of the imaging opticalsystem, a focus detector that detects a focus adjustment state at theimaging optical system based upon a shift amount between a pair ofimages formed with light fluxes passing through a pair of areas on apupil of the imaging optical system, and a focus adjustment controllerthat executes focus adjustment for the imaging optical system based uponthe focus adjustment state detected by the image sensor or the focusdetector selected in correspondence to photographic conditions.

The imaging device may further comprise an optical element capable ofdirecting a light flux from the imaging optical system along a lightpath extending toward the image sensor and along a light path extendingtoward the focus detector.

The image sensor in the imaging device may include the imaging pixelsand the focus detection pixels disposed on a single substrate.

The focus detection pixels may each include a micro-lens and a pair ofphotoelectric conversion units provided in correspondence to themicro-lens.

The focus detector may include a pair of secondary focusinglens/re-focusing lens for reforming an image formed at a predeterminedimage plane of the imaging optical system and an image sensor thatdetects images reformed via the pair of re-focusing lenses.

According to the 8th aspect of the invention, an imaging device comprisean image sensor that includes imaging pixels for capturing an imageformed via an imaging optical system and focus detection pixels fordetecting a focus adjustment state at the imaging optical system basedupon a shift amount between a pair of images formed with light fluxespassing through a pair of areas on a pupil of the imaging opticalsystem, a focus detector that detects the focus adjustment state at theimaging optical system based upon a shift amount between a pair ofimages formed with light fluxes passing through a pair of areas on apupil of the imaging optical system, and a focus adjustment controllerthat executes focus adjustment for the imaging optical system based uponthe focus adjustment state detected by one of the image sensor and thefocus detector selected in correspondence to photographic conditions.The focus adjustment controller executes focus adjustment for theimaging optical system based upon the focus adjustment state detected bythe focus detector until an imaging operation starts and executes focusadjustment for the imaging optical system based upon the focusadjustment state detected by the image sensor once the imaging operationstarts.

According to the 9th aspect of the invention, an imaging devicecomprises an image sensor that includes imaging pixels for capturing animage formed via an imaging optical system and focus detection pixelsfor detecting a focus adjustment state at the imaging optical systembased upon a shift amount between a pair of images formed with lightfluxes passing through a pair of areas on a pupil of the imaging opticalsystem, a focus detector that detects the focus adjustment state at theimaging optical system based upon a shift amount between a pair ofimages formed with light fluxes passing through a pair of areas on thepupil of the imaging optical system, and a focus adjustment controllerthat executes focus adjustment for the imaging optical system based uponthe focus adjustment state detected by one of the image sensor and thefocus detector selected in correspondence to photographic conditions.The focus adjustment controller executes focus adjustment for theimaging optical system based upon the focus adjustment state detected bythe focus detector while a continuous shooting is in progress.

According to the 10th aspect of the invention, an imaging devicecomprises an image sensor that includes imaging pixels for capturing animage formed via an imaging optical system and focus detection pixelsfor detecting a focus adjustment state at the imaging optical systembased upon a shift amount between a pair of images formed with lightfluxes passing through a pair of areas on a pupil of the imaging opticalsystem, a focus detector that detects a focus adjustment state at theimaging optical system based upon a shift amount between a pair ofimages formed with light fluxes passing through a pair of areas on apupil of the imaging optical system, and a focus adjustment controllerthat executes focus adjustment for the imaging optical system based uponthe focus adjustment state detected by one of the image sensor and thefocus detector selected in correspondence to photographic conditions.The focus adjustment controller executes focus adjustment for theimaging optical system based upon the focus adjustment state detected bythe focus detector while a movie shooting is in progress.

The focus adjustment controller may execute focus adjustment for theimaging optical system based upon the focus adjustment state detected bythe image sensor while a continuous shooting is in progress with thelight path of the imaging optical system directed toward the imagesensor by the optical element.

The focus adjustment controller may execute focus adjustment for theimaging optical system based upon the focus adjustment state detected bythe image sensor while a movie shooting is in progress with the lightpath of the imaging optical system directed toward the image sensor bythe optical element.

The focus adjustment controller may execute focus adjustment based uponthe focus adjustment state detected by the focus detector when detectingthe focus adjustment state in a plurality of focus detection areascorresponding to a plurality of positions set on a predetermined imageplane of the imaging optical system, and execute focus adjustment basedupon the focus adjustment state detected by the image sensor whendetecting the focus adjustment state in one of the plurality of focusdetection areas.

The focus adjustment controller may execute focus adjustment based uponthe focus adjustment state detected by the focus detector whencontinuously executing the focus adjustment after the imaging opticalsystem is in focus, and execute focus adjustment based upon the focusadjustment state detected by the image sensor if the focus adjustment isdisallowed once the imaging optical system is in focus.

The imaging device may further comprise a display at which the focusadjustment state detected by the image sensor is indicated when focusadjustment is manually executed.

The imaging device may further comprise a monitor at which an imagecaptured by the image sensor is displayed. In this case, the focusadjustment controller can execute focus adjustment based upon the focusadjustment state detected by the image sensor when magnifying anddisplaying the image captured by the image sensor at the monitor, andexecute focus adjustment based upon the focus adjustment state detectedby the focus detector when reducing and displaying the image at themonitor.

According to the 11th aspect of the invention, an imaging devicecomprises an image sensor that includes imaging pixels for capturing animage formed via an imaging optical system and focus detection pixelsfor detecting a focus adjustment state at the imaging optical systembased upon a shift amount between a pair of images formed with lightfluxes passing through a pair of areas on a pupil of the imaging opticalsystem, a focus detector that detects a focus adjustment state at theimaging optical system based upon a shift amount between a pair ofimages formed with light fluxes passing through a pair of areas on thepupil of the imaging optical system, and a focus adjustment controllerthat executes focus adjustment for the imaging optical system based uponthe focus adjustment state detected by one of the image sensor and thefocus detector selected in correspondence to photographic conditions.The focus adjustment controller executes focus adjustment based upon thefocus adjustment state detected by the image sensor when a minimumf-number of the imaging optical system indicates a level brighter than alevel corresponding to a predetermined value, and executes focusadjustment based upon the focus adjustment state detected by the focusdetector when the minimum f-number indicates a level darker than thelevel corresponding to the predetermined value.

The focus adjustment controller may execute focus adjustment based uponthe focus adjustment state detected by the image sensor when an aperturevalue used to control the image optical system indicates a levelbrighter than a level corresponding to a predetermined value, andexecute focus adjustment based upon the focus adjustment state detectedby the focus detector when the aperture used to control the imagingoptical system indicates a level darker than the level corresponding tothe predetermined value.

The focus adjustment controller may execute focus adjustment based uponthe focus adjustment state detected by the image sensor when a focallength of the imaging optical system is smaller than a predeterminedvalue, and execute focus adjustment based upon the focus adjustmentstate detected by the focus detector when the focal length is greaterthan the predetermined value.

The focus adjustment controller may execute focus adjustment based uponthe focus adjustment state detected by the image sensor when an exposuretime set for an imaging operation executed at the image sensor isshorter than a predetermined length of time, and execute focusadjustment based upon the focus adjustment state detected by the focusdetector when the exposure time is longer than the predetermined lengthof time.

The focus adjustment controller may execute focus adjustment based uponthe focus adjustment state detected by the image sensor when asensitivity is lower than a predetermined value, and execute focusadjustment based upon the focus adjustment state detected by the focusdetector if the sensitivity is higher than the predetermined value.

The focus adjustment controller may execute focus adjustment based uponthe focus adjustment state detected by the image sensor when aphotographic subject is not illuminated during a photographingoperation, and execute focus adjustment based upon the focus adjustmentstate detected by the focus detector when the photographic subject isilluminated during the photographing operation.

The focus adjustment controller may execute focus adjustment based uponthe focus adjustment state detected by the image sensor when aself-timer photographing mode is selected, and execute focus adjustmentbased upon the focus adjustment state detected by the focus detectorwhen the self-timer photographing mode is not selected.

The focus adjustment controller may execute focus adjustment based uponthe focus adjustment state detected by the image sensor when the imagingdevice is set at a fixed position, and execute focus adjustment basedupon the focus adjustment state detected by the focus detector when theimaging device is not fixed.

The focus adjustment controller may execute focus adjustment based uponthe focus adjustment state detected by the image sensor when a mode forphotographing a stationary subject is set, and execute focus adjustmentbased upon the focus adjustment state detected by the focus detectorwhen a mode for photographing a moving subject is set.

According to the 12th aspect of the invention, an imaging devicecomprises an image sensor that includes imaging pixels for capturing animage formed via an imaging optical system and focus detection pixelsfor detecting a focus adjustment state at the imaging optical systembased upon a shift amount between a pair of images formed with lightfluxes passing through a pair of areas on a pupil of the imaging opticalsystem, a focus detector that detects a focus adjustment state at theimaging optical system based upon a shift amount between a pair ofimages formed with light fluxes passing through a pair of areas on apupil of the imaging optical system, and a focus adjustment controllerthat executes focus adjustment for the imaging optical system based uponthe focus adjustment state detected by one of the image sensor and thefocus detector selected in correspondence to photographic conditions.The focus adjustment controller executes focus adjustment based upon thefocus adjustment state detected by the focus detector when the focusadjustment state indicates a value greater than a predetermined value,and executes focus adjustment based upon the focus adjustment statedetected by the image sensor when the focus adjustment state indicates avalue smaller than the predetermined value.

The focus adjustment controller may execute focus adjustment based uponthe focus adjustment state detected by the image sensor when abrightness in an image field is higher than a predetermined value, andexecute focus adjustment based upon the focus adjustment state detectedby the focus detector when the brightness in the image field is lowerthan the predetermined value.

The imaging device may further comprise a judging circuit that judges asto whether a photographic subject is stationary or moving. In this case,the focus adjustment controller may execute focus adjustment based uponthe focus adjustment state detected by the image sensor if the judgingcircuit determines that the photographic subject is stationary, andexecute focus adjustment based upon the focus adjustment state detectedby the focus detector if the judging circuit determines that thephotographic subject is moving.

The focus adjustment controller may execute focus adjustment based uponthe focus adjustment state detected by the image sensor when noauxiliary light is radiated for focus detection, and executes focusadjustment based upon the focus adjustment state detected by the focusdetector when the auxiliary light is radiated.

According to the 13th aspect of the invention, a focus adjustment methodcomprises providing an image sensor that includes imaging pixels forcapturing an image formed via an imaging optical system and focusdetection pixels for detecting a focus adjustment state at the imagingoptical system through a first processing process, providing a focusdetector that detects a focus adjustment state at the imaging opticalsystem through a second processing process different from the firstprocessing process, and executing focus adjustment for the imagingoptical system based upon the focus adjustment states detected by theimage sensor and the focus detector.

According to the 14th aspect of the invention, a focus adjustment methodcomprises providing an image sensor that includes imaging pixels forcapturing an image formed via an imaging optical system and focusdetection pixels for detecting a focus adjustment state at the imagingoptical system, providing a focus detector that detects a focusadjustment state at the imaging optical system, and executing focusadjustment for the imaging optical system based upon the focusadjustment states detected by the image sensor and the focus detector.Focus adjustment is executed based upon the focus adjustment statedetected by the focus detector when the focus adjustment state indicatesa value greater than a predetermined value and focus adjustment isexecuted based upon the focus adjustment state detected by the imagesensor when the focus adjustment state indicates a value smaller thanthe predetermined value.

According to the 15th aspect of the invention, an imaging methodcomprising providing an image sensor that includes imaging pixels forcapturing an image formed via an imaging optical system and focusdetection pixels for detecting a focus adjustment state at the imagingoptical system based upon a shift amount between a pair of images formedwith light fluxes passing through a pair of areas on a pupil of theimaging optical system, providing a focus detector that detects a focusadjustment state at the imaging optical system based upon a shift amountbetween a pair of images formed with light fluxes passing through a pairof areas on a pupil of the imaging optical system, and executing focusadjustment for the imaging optical system based upon the focusadjustment state detected by one of the image sensor and the focusdetector selected in correspondence to photographic conditions.

According to the 16th aspect of the invention, an imaging methodcomprises providing an image sensor that includes imaging pixels forcapturing an image formed via an imaging optical system and focusdetection pixels for detecting a focus adjustment state at the imagingoptical system based upon a shift amount between a pair of images formedwith light fluxes passing through a pair of areas on a pupil of theimaging optical system, providing a focus detector that detects a focusadjustment state at the imaging optical system based upon a shift amountbetween a pair of images formed with light fluxes passing through a pairof areas on a pupil of the imaging optical system, and executing focusadjustment for the imaging optical system based upon the focusadjustment state detected by one of the image sensor and the focusdetector selected in correspondence to photographic conditions. Focusadjustment for the imaging optical system is executed based upon thefocus adjustment state detected by the focus detector until an imagingoperation starts, and focus adjustment for the imaging optical system isexecuted based upon the focus adjustment state detected by the imagesensor once the imaging operation starts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the structure adopted in the digital still camera in anembodiment;

FIG. 2 is a front view showing in detail the structure of the imagesensor;

FIG. 3 is a sectional view of an imaging pixel;

FIG. 4 is a sectional view of a focus detection pixel;

FIG. 5 illustrates a pupil division-type phase difference detectionmethod achieved in conjunction with micro-lenses;

FIG. 6 is a front view, showing the relationship between the projectionareas (range-finding pupils) of the pair of photoelectric conversionunits in a focus detection pixel over the exit pupil plane;

FIG. 7 shows the circuit structure of the image sensor;

FIG. 8 shows in detail the structure adopted in a focus detection sensorcorresponding to that shown in FIG. 1;

FIG. 9 shows the range-finding pupils on the exit pupil plane in animage reformation method;

FIG. 10 shows the circuit structure of an image sensor constituting partof a focus detection sensor used for an exclusive AF operation;

FIG. 11 shows the focus detection positions assumed on the photographicimage plane;

FIG. 12 presents a flowchart of the operations executed in the digitalstill camera (imaging device) in FIG. 1;

FIG. 13 presents a flowchart of the image shift amount detectionoperation;

FIG. 14 presents a flowchart of the operation executed to convert theimage shift amount to a defocus amount;

FIG. 15 presents a flowchart of the verification operation executed toverify the photographic subject capturing AF area;

FIG. 16 illustrates the focus detection calculation algorithm;

FIG. 17 presents a flowchart of the focus detection operation;

FIG. 18 presents another positional arrangement example that may beadopted in conjunction with the focus detection sensor (exclusive AF)and the image sensor (image sensor AF);

FIG. 19 presents yet another positional arrangement example that may beadopted in conjunction with the focus detection sensor (exclusive AF)and the image sensor (image sensor AF); and

FIG. 20 presents yet another positional arrangement example that may beadopted in conjunction with the focus detection sensor (exclusive AF)and the image sensor (image sensor AF).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An explanation is now given on the focus detection device according tothe present invention and a digital still camera representing an exampleof an imaging device equipped with the focus detection device.

FIG. 1 shows the structure adopted in the digital still camera in anembodiment. A digital still camera 201 comprises an exchangeable lens202 and a camera body 203. The exchangeable lens 202 is mounted at thecamera body 203 via a mount unit 204.

The exchangeable lens 202 includes an objective lens 209, a zooming lens208, a focusing lens 210, an aperture 211 and a lens drive controlcircuit 206. The lens drive control circuit 206, which includes a CPUand a drive circuit (neither shown), controls the drive of the focusinglens 210 and the aperture 211, detects the states of the zooming lens208, the focusing lens 210 and the aperture 211, and exchanges lensinformation and focus adjustment information by communicating with abody CPU 214 to be detailed later.

In the camera body 203, a half mirror 205, a focus detection sensor 207,an image sensor 212, the body CPU 214, an LCD driver 215, an LCD 216, aneyepiece lens 217, a memory card 219, a drive control circuit 220, anexternal operation member 221 and the like are installed.

At the half mirror 205 disposed on the optical axis of the exchangeablelens 202, a light path is split to a reflection-side path and atransmission-side path. A half mirror function of the half mirror 205 isachieved by forming a reflecting film over the front surface of a glassplate with a predetermined thickness, with an anti-reflection filmformed over the rear surface of the glass plate. The focus detectionsensor 207, disposed on the transmission side path from the half mirror205 at an estimated focus plane (predetermined image forming plane) ofthe exchangeable lens 202 has a function of detecting the focus of theexchangeable lens 202. The focus detection sensor 207 includes aplurality of built-in focus detection units (not shown) adopting animage reformation method, so as to execute focus detection at aplurality of focus detection positions.

The image sensor 212 disposed on the reflection-side path from the halfmirror 205 at an estimated focus plane of the exchangeable lens 202, hasa function of detecting the focus of the exchangeable lens 202 and animaging function.

The image sensor 212 includes two-dimensionally arrayed imaging pixelsand a row of focus detection pixels set in the imaging pixel array overareas corresponding to a plurality of focus detection positions.

In this specification, the focus adjustment executed for the focusinglens 210 based upon the focus detection results provided by the focusdetection sensor 207 is referred to as “exclusive AF” or “imagereformation method AF”, since the focus is adjusted via the specialfocus detection sensor exclusively used for focus detection. Inaddition, the focus adjustment executed for the focusing lens 210 basedupon the focus detection results obtained from the focus detection pixelrows at the image sensor 212 is referred to as “image sensor AF” or“micro-lens method AF” since the focus is adjusted via the image sensorin this case.

The body CPU 214 controls the read operation executed to read out theoutputs from the image sensor 212 and the focus detection sensor 207,communicates with the lens drive control circuit 206 (to exchange thelens information/focus adjustment information), controls the switch-overfrom the image sensor 212 to the focus detection sensor 207 and viceversa when adjusting the focus for the exchangeable lens 202, controlsthe focus detection and the focus adjustment for the exchangeable lens202, controls the imaging operation executed to capture an image, andcontrols the overall operations of the digital still camera. The bodyCPU 214 and the lens drive control circuit 206 exchange various types ofinformation, such as the lens information and information indicating thedefocus amount based upon which the focusing lens is driven, via anelectrical contact point portion 213 present at the mount unit 204.

The LCD 216 functions as a liquid crystal viewfinder (EVF: electronicviewfinder). The LCD driver 215 drives the LCD 216 to display a capturedimage or various types of information including photographic conditions.The photographer is able to see such information via the eyepiece lens217. The memory card 219 is used as an image storage area in which imagesignals are stored. The drive control circuit 220 includes circuitsengaged in operation to control the camera, such as a timer. Inaddition, the external operation member 221 includes operating membersoperated to perform various types of operations and select varioussettings, such as a shutter button, in the digital camera.

A subject image formed on the image sensor 202, after passing throughthe exchangeable lens 202 and being reflected at the half mirror 205,then undergoes photoelectric conversion at the image sensor 212. Signalsresulting from the photoelectric conversion are then transmitted to thebody CPU 214. A subject image formed on the focus detection sensor 207,after passing through the exchangeable lens 202 and being transmittedthrough the half mirror 205, on the other hand, undergoes photoelectricconversion at an image sensor built into the focus detection sensor 207.The signals resulting from the photoelectric conversion at the imagesensor are then transmitted to the body CPU 214.

The body CPU 214 executes focus detection calculation based upon theoutput from the focus detection pixel row at the image sensor 212 andthe output from the focus detection sensor 207 and determines the stateof the focus adjustment achieved with regard to the image formed on theimage sensor 212 via the exchangeable lens 202, i.e., determines thedefocus amount indicating the extent of defocusing. The defocus amountthus calculated is provided to the lens drive control circuit 206. Inaddition, the body CPU 214 stores image signals generated based upon theoutputs from the imaging pixels into the memory card 219, and alsodetermines through an arithmetic operation the brightness of thephotographic field by photometering the photographic field based uponthe outputs from the imaging pixels and the focus detection pixels. Thebody CPU 214 also transmits the image signals to the LCD driver 215,which then displays the image at the LCD 216. Furthermore, in responseto signals from the drive control circuit 220, the body CPU 214 effectsswitch-overs for various types of control or starts up any of thevarious types of control. It also effects switch-overs for the varioustypes of control in response to switching operations performed at theexternal operation member 221 or in correspondence to the specificoperational status assumed at the external operation member 221.

The CPU (not shown) in the lens drive control circuit 206 adjusts thelens information in correspondence to the current focusing state,zooming state, aperture setting state and the like. More specifically,it monitors the positions of the zooming lens 208 and the focusing lens210 and the position of the aperture 211, and calculates correct lensinformation based upon the monitored information. Alternatively, it mayselect the lens information corresponding to the monitored informationfrom a lookup table prepared in advance. In addition, the lens drivecontrol circuit 206 calculates a lens drive quantity indicating theextent to which the lens is to be driven based upon the defocus amounthaving been received and drives the focusing lens 210 to a focus matchpoint based upon the lens drive quantity.

The following advantages are achieved by adopting the structure shown inFIG. 1 in the digital camera in the embodiment with the image sensor 212disposed on the reflection side of the half mirror 205 and the focusdetection sensor 207 disposed on the transmission side of the halfmirror 205. Namely, since the half mirror 205 does not need to retreatfor each imaging operation, quick response is assured when capturing animage, which allows the photographer to make the most of a good photoopportunity with a high level of reliability. In addition, since thequality of the captured image is not lowered due to aberrationdeterioration as the image is transmitted through the half mirror 205, ahigher-quality image compared to the image captured on the transmissionside, can be captured at the image sensor. Moreover, the focus can beadjusted through the exclusive AF concurrently while the imagingoperation is in progress.

FIG. 2 is a front view showing in detail the structure of the imagesensor 212. The image sensor 212 comprises imaging pixels 310 and focusdetection pixels 311. As shown in FIG. 2A, the imaging pixels 310 arearrayed two-dimensionally, whereas the focus detection pixels 311 aredisposed over areas corresponding to the five focus detection positionsindicated as P11 to P15 in FIG. 11B. The imaging pixels 310 each includea micro-lens 10 and a photoelectric conversion unit 11 used for imagingpurposes, as shown in FIG. 2B. The focus detection pixels 311 eachinclude a micro-lens 10 and a pair of photoelectric conversion units 12and 13 used for focus detection purposes, as shown in FIG. 2C.

FIG. 3 is a sectional view of an imaging pixel 310. The micro-lens 10 isset to the front of the imaging photoelectric conversion unit 11 at theimaging pixel 310 and, as a result, the image of the photoelectricconversion unit 11 is projected frontward via the micro-lens 10. Thephotoelectric conversion unit 11 is formed on a semiconductor circuitsubstrate 29.

FIG. 4 is a sectional view of a focus detection pixel 311. In the focusdetection pixel 311, the micro-lens 10 is disposed to the front of thephotoelectric conversion units 12 and 13 used for focus detection andthus, the photoelectric conversion units 12 and 13 are projectedfrontward via the micro-lens 10. Images of the photoelectric conversionunits 12 and 13 are formed on the same semiconductor circuit substrate29. It is to be noted that the micro-lenses 10 disposed at the front ofthe imaging pixel 310 and the focus detection pixel 311 are positionedon the estimated focus plane of the exchangeable lens 202.

FIG. 5 illustrates a pupil division-type phase difference detectionmethod achieved in conjunction with the micro-lenses. It is to be notedthat FIG. 5 shows only some of the focus detection pixels 311(micro-lenses 50 and 60 and two pairs of photoelectric conversion units52/53 and 62/63). Reference numeral 90 indicates the exit pupil set overa distance d4 along the frontward direction from the micro-lenses 50 and60 disposed on the estimated focus plane of the exchangeable lens 202.It is to be noted that the distance d4 is determined in correspondenceto the curvature of the micro-lenses, the refractive index of themicro-lenses, the distance between the micro-lenses and thephotoelectric conversion units and the like. The distance d4 between theestimated focus plane of the exchangeable lens 202 and the exit pupil isreferred to as a range-finding pupil distance in this specification.

Reference numeral 91 indicates the optical axis of the exchangeable lens202. Reference numeral 92 indicates a range (range-finding pupil)defined by the photoelectric conversion units 52 and 62 projected viathe micro-lenses 50 and 60, whereas reference numeral 93 indicates therange (range-finding pupil) defined by the photoelectric conversionunits 53 and 63 projected via the micro-lenses 50 and 60. The two pairsof focus detection light fluxes 72/73 and 82/83 from the subject havingpassed through the pair of range-finding pupil ranges 92 and 93 reachthe two pairs of photoelectric conversion units 52/53 and 62/63 via themicro-lenses 50 and 60 respectively.

FIG. 5 schematically shows the focus detection pixel 311 (constitutedwith the micro-lens 50 and the pair of photoelectric conversion units 52and 53) set on the optical axis 91 and the focus detection pixel 311(constituted with the micro-lens 60 and the pair of photoelectricconversion units 62 and 63) set off the optical axis. In each of theother focus detection pixels 311, too, the focus detection light fluxesreaching the micro-lens from a pair of range-finding pupils are receivedat the pair of photoelectric conversion units. It is to be noted thatthe focus detection pixels 311 are arrayed along the direction matchingthe direction in which the pair of range-finding pupils are separatedfrom each other.

The micro-lenses 50 and 60 are set near the estimated focus plane of theexchangeable lens 202. The shapes of the pair of photoelectricconversion units 52 and 53 disposed behind the micro-lens 50 set on theoptical axis 91 are projected via the micro-lens 50 onto the exit pupil90 set apart from the micro-lenses 50 and 60 by the projection distanced4 and the projected shapes define the range-finding pupils 92 and 93.

The shapes of the pair of photoelectric conversion units 62 and 63disposed behind the micro-lens 60 set off the optical axis 91 areprojected via the micro-lens 60 onto the exit pupil 90 set apart by theprojection distance d4 and the projected shapes define the range-findingpupils 92 and 93. Namely, the projecting direction for each pixel isdetermined so that the projected shapes (range-finding pupils 92 and 93)of the photoelectric conversion units in the individual pixels arealigned on the exit pupil 90 set over the range-finding pupil distanced4.

The photoelectric conversion unit 52 outputs a signal corresponding tothe intensity of an image formed on the micro-lens 50 with the focusdetection light flux 72 having passed through the range-finding pupil 92and having advanced toward the micro-lens 50. In addition, thephotoelectric conversion unit 53 outputs a signal corresponding to theintensity of an image formed on the micro-lens 50 with the focusdetection light flux 73 having passed through the range-finding pupil 93and having advanced toward the micro-lens 50.

Also, the photoelectric conversion unit 62 outputs a signalcorresponding to the intensity of an image formed on the micro-lens 60with the focus detection light flux 82 having passed through therange-finding pupil 92 and having advanced toward the micro-lens 60. Thephotoelectric conversion unit 63 outputs a signal corresponding to theintensity of an image formed on the micro-lens 60 with the focusdetection light flux 83 having passed through the range-finding pupil 93and having advanced toward the micro-lens 60.

By arranging numerous focus detection pixels 311 each structured asdescribed above and integrating the outputs from the pairs ofphotoelectric conversion units 12 and 13 disposed behind the focusdetection pixels 311, into output groups each corresponding to one ofthe two range-finding pupils 92 and 93 respectively, information relatedto the intensity distribution of the pair of images formed on the pixelrow with the individual focus detection light fluxes passing through therange-finding pupil 92 and the range-finding pupil 93 is obtained. Next,image shift detection arithmetic processing (correlational processing,phase difference detection processing) to be detailed later, is executedby using the information thus obtained so as to detect the shift amountbetween the pair of images through the pupil division-type phasedifference detection method.

The image shift amount is then multiplied by a predetermined conversioncoefficient and, as a result, the extent of deviation (defocus amount)of the current image forming plane relative to the estimated focus planecan be calculated. It is to be noted that the defocus amount assumesdifferent values at various focus detection positions. The accuracy withwhich the defocus amount (image shift amount) is detected is determinedin correspondence to the image shift amount detection pitch and when thefocus detection is executed by using micro-lenses, the detectionaccuracy is determined in correspondence to the pitch at which themicro-lenses are set.

FIG. 6 is a front view showing the relationship between the projectionranges (range-finding pupils) over which the pair of photoelectricconversion units 12 and 13 in a focus detection pixel 311 are projectedon the exit pupil plane 90. A circumscribing circle 94 circumscribingthe range-finding pupils 92 and 93 (indicated by the solid lines) formedby projecting the pair of photoelectric conversion units 12 and 13 inthe focus adjustment pixel 311 onto the exit pupil plane 90 via themicro-lens 10, as viewed from the estimated focus plane, assumes aspecific minimum f-number (maximum aperture). In the specification, theminimum f-number is referred to as a range-finding pupil f-number. Undernormal circumstances, if the minimum f-number of the aperture opening inthe exchangeable lens 202 corresponds to a brightness level higher thanthat corresponding to the range-finding pupil f-number, the focusdetection light fluxes are not blocked at the aperture opening at theexchangeable lens 202 and, as a result, highly accurate focus detectionis enabled.

If the distance to the exit pupil, which corresponds to the apertureopening at the exchangeable lens 202, does not match the range-findingpupil distance, the focus detection accuracy is lowered for thefollowing reasons. Namely, when detecting the focus at a position in theperiphery of the image plane, the focus detection light fluxes may bepartially blocked at pixels present in the periphery of the image planeeven if the minimum f-number of the aperture opening at the exchangeablelens 202 indicates a brightness higher than that corresponding to therange-finding pupil f-number. In FIG. 6, points 95 and 96 indicate thepositions of the gravitational centers of the range-finding pupils 92and 93 taken along the direction in which the range-finding pupils areset next to each other (along the x direction). The value selected forthe conversion coefficient used to convert the image shift amount to thedefocus amount is determined in correspondence to the opening angleformed by viewing the gravitational center positions 95 and 96 from thefocus detection position on the estimated focus plane. The focusdetection accuracy improves as the opening angle increases, whereas thedefocus amount detection range increases as the opening angle becomessmaller.

It is to be noted that FIG. 6 shows the range-finding pupilscorresponding to the focus detection positions P11, P12 and P13 in FIG.11B. The range-finding pupils corresponding to the focus detectionpositions P14 and P15 are formed at positions reached by rotating therange-finding pupils in FIG. 6 by 90° and the circle (range-findingpupil f-number) circumscribing these range-finding pupils is identicalto that shown in FIG. 6.

FIG. 7 shows the circuit structure adopted in the image sensor 212. Theimage sensor 212 includes a read circuit through which the outputsignals from the photoelectric conversion units are read out. Referencenumeral 26 indicates the photoelectric conversion unit (equivalent to 11in FIGS. 2 and 3) a teach imaging pixel 310, whereas reference numerals27 and 28 indicate a pair of photoelectric conversion units (equivalentto 12 and 13 in FIGS. 2 and 4) in each focus detection pixel 311. Avertical transfer register 20 turns on/off transfer MOS switches 24 eachprovided in correspondence to one of the photoelectric conversion units26, 27 and 28 and transfers the outputs from the photoelectricconversion units 26 to 28 to transfer MOS switches 25 in units of theindividual pixel lines.

A horizontal transfer register 21 sequentially turns on/off the transferMOS switches 25 and thus sequentially transfers the outputs having beentransferred via the transfer MOS switches 24 to an amplifier 23. Theamplifier 23 amplifies the outputs transferred via the transfer MOSswitches 25 and outputs the amplified outputs to the outside of theimage sensor 212. The photoelectric conversion units, the transfer MOSswitches, the registers and the amplifier are all formed on thesemiconductor substrate 29.

The manufacturing costs can be reduced by using the image sensors 212 toconstitute a MOS image sensor instead of a CCD image sensor. Since thefocus detection pixels are also constituted with MOS image sensors, datafrom the specific focus detection pixels corresponding to the selectedfocus detection position alone can be read out at high speed.

FIG. 8 shows in detail the structure adopted in the focus detectionsensor 207 shown in FIG. 1. An explanation is now given on a focusdetection method adopting an image reformation system in reference toFIG. 8. In FIG. 8, reference numeral 91 indicates the optical axis ofthe exchangeable lens 202, reference numerals 110 and 120 each indicatea condenser lens, reference numerals 111 and 121 each indicate anaperture mask, reference numerals 112, 113, 122 and 123 each indicate anaperture opening, reference numerals 114, 115, 124 and 125 each indicatean image reforming lens, reference numerals 116 and 126 each indicate animage sensor (CCD) engaged in focus detection, and reference numerals132, 133, 142 and 143 each indicate a focus detection light flux.

Reference numeral 101 indicates an exit pupil set over a distance d5along the forward direction from the estimated focus plane of theexchangeable lens 202. The distance d5, which is determined incorrespondence to the focal lengths of the condenser lenses 110 and 120,the distances from the condenser lenses 110 and 120 to the apertureopenings 112, 113, 122 and 123 and the like, is to be referred to as arange-finding pupil distance. Reference numeral 102 indicates the range(range-finding pupil) defined by the aperture openings 112 and 122projected via the condenser lenses 110 and 120, whereas referencenumeral 103 indicates the range (range-finding pupil) defined by theaperture openings 113 and 123 projected via the condenser lenses 110 and120. The condenser lens 110, the aperture mask 111, the apertureopenings 112 and 113, the image reforming lenses 114 and 115 and theimage sensor 116 constitute a focus detection unit engaged in a pupildivision-type phase difference detection by adopting the imagereformation method through which the focus detection is executed at agiven position.

FIG. 8 schematically illustrates the focus detection unit present on theoptical axis 91 and a focus detection unit present off the optical axis91. By using a plurality of focus detection units in combination,exclusive AF for executing focus detection at the five focus detectionpositions P1 to P5 through the pupil division-type phase differencedetection adopting the image reformation method is realized as shown inFIG. 11A. The focus detection unit present on the optical axis 91includes the condenser lens 110 disposed near the estimated focus planeof the exchangeable lens 202, the image sensor 116 disposed behind thecondenser lens, the pair of image reforming lenses 114 and 115 and theaperture mask 111. A primary image formed near the estimated focus planeis reformed onto the image sensor 116 via the pair of image reforminglenses 114 and 115 disposed between the condenser lens 110 and the imagesensor 116. The aperture mask 111 includes a pair of aperture openings112 and 113 set near (to the front in the figure) the pair of imagereforming lenses 114 and 115.

The image sensor 116 is a line sensor that includes a plurality ofphotoelectric conversion units densely set along a straight line. Thephotoelectric conversion units in the image sensor are set next to oneanother along the direction matching the direction in which the pair ofrange-finding pupils are separated from each other (along the directionin which the aperture openings are set next to each other). Informationcorresponding to the light intensity distribution of the pair of imagesreformed on the image sensor 116 is output from the image sensor 116.Image shift detection arithmetic processing (correlational processing,phase difference detection processing) to be detailed later is thenexecuted by using the information thus output so as to detect the extentof image shift between the pair of images through the pupildivision-type phase difference detection method. The image shift amountis multiplied by a predetermined conversion coefficient and, as aresult, the extent of deviation (defocus amount) of the current imageforming plane relative to the estimated focus plane can be calculated.

The image sensor 116 is projected onto the estimated focus plane via theimage reforming lenses 114 and 115, and the accuracy with which thedefocused amount (image shift amount) is detected is determined incorrespondence to the image shift amount detection pitch (the pitch atwhich the photoelectric conversion units, projected onto the estimatedfocus plane, are disposed in the image reformation method). The apertureopenings 112 and 113 in the aperture mask 111 are projected via thecondenser lens 110 to range over the areas 102 and 103 on the exit pupil101. These areas 102 and 103 are referred to as range-finding pupils. Inother words, the pair of images reformed on the image sensor 116 areformed with light fluxes passing through the pair of range-findingpupils 102 and 103 on the exit pupil 101. The light fluxes 132 and 133passing through the pair of range-finding pupils 102 and 103 on the exitpupil 101 are referred to as focus detection light fluxes.

FIG. 9 shows the range-finding pupils formed on the exit pupil plane byadopting the image reformation method. A circle 84 circumscribing therange-finding pupils 102 and 103 (indicated by the solid lines) whichare formed by projecting the pair of aperture openings onto the exitpupil plane 101 via the condenser lens, when viewed from the estimatedfocus plane, assumes a specific minimum f-number (range-finding pupilf-number). The range-finding pupil f-number is set in the imagereformation method to a level darker (a larger f-number) than the levelcorresponding to the range-finding pupil f-number selected in themicro-lens method shown in FIG. 6.

Points 85 and 86 indicate the positions of the gravitational centers ofthe range-finding pupils 102 and 103 taken along the direction (xdirection) in which the range-finding pupils are formed side-by-side.The value of the conversion coefficient used to convert the image shiftamount to the defocus amount is determined in correspondence to theopening angle formed by viewing the gravitational center positions 85and 86 from the focus detection position on the estimated focus plane. Asmaller opening angle is set in the image reformation method compared tothe opening angle set in the micro-lens method shown in FIG. 6, so as toenable detection of a large defocus amount. It is to be noted that FIG.9 shows the range-finding pupils corresponding to the focus detectionpositions P1, P2 and P3 in FIG. 11A. The range-finding pupilscorresponding to the focus detection positions P4 and P5 are formed atpositions reached by rotating the range-finding pupils in FIG. 9 by 90°and the circle (range-finding pupil f-number) circumscribing theserange-finding pupils is identical to that shown in FIG. 9.

FIG. 10 shows the circuit structure adopted in the image sensor (CCD) ofthe focus detection sensor 207 used in the exclusive AF operation.Reference numerals 30 and 31 indicate a pair of photoelectric conversionunit rows corresponding to one focus detection position, referencenumeral 32 indicates a CCD transfer register that transfers the outputsfrom the pair of photoelectric conversion unit rows 30 and 31, andreference numeral 33 indicates an amplifier that amplifies the outputstransferred from the CCD transfer register 32 and outputs the amplifiedoutputs to the outside. The CCD image sensor 117 includes fivestructural units each comprising the pair of photoelectric conversionunit rows, the CCD transfer register and the amplifier as describedabove in correspondence to the five focus detection positions shown inFIG. 11A.

The operational control in each structural unit, including the controlon the length of the electrical charge storage time, the output transferoperation and the amplification operation, can be executed by itselfcompletely independently. Since the operational control on thephotoelectric conversion units corresponding to the plurality of focusdetection positions can be executed independently of one another, it ispossible to obtain outputs at the optimal level by independentlycontrolling the lengths of the charge storage periods in correspondenceto the brightness levels even when the levels of brightness vary greatlyat the plurality of focus detection positions. This structure is idealin applications in which focus detection is executed simultaneously atall the focus detection positions.

FIG. 11 shows the focus detection positions set within the imaging plane100 on the estimated focus plane of the exchangeable lens 202. FIG. 11Ashows areas (focus detection areas) where the image is sampled withinthe imaging plane 100 when the focus detection is executed with thefocus detection sensor 207 through the pupil division-type phasedifference detection by adopting the image reformation method. In theimage reformation method, the photoelectric conversion unit rows at theimage sensor are projected onto the image plane 100 and these projectionareas are used as the focus detection areas. Accordingly, the samplingpitch as well as the length and width of the focus detection areas aredetermined in correspondence to the size of the photoelectric conversionunits, the length of the photoelectric conversion unit rows, the pitchat which the individual photoelectric conversion units are disposed, andthe projection magnification factor of the image reforming lenses.

FIG. 11B shows areas (focus detection areas) where the image is sampledwithin the imaging plane 100 when executing the focus detection in themacro-lens method. In the macro-lens method, the rows of micro-lensesare used as the focus detection areas on the image plane 100.Accordingly, the sampling pitch as well as the length and width of thefocus detection areas is determined in correspondence to the size of themicro-lenses, the length of the micro-lens rows and the pitch at whichthe individual micro-lenses are disposed to form the micro-lens rows.

FIG. 11C shows the focus detection areas defined in the imagereformation method (exclusive AF) and the micro-lens method (imagesensor AF) superimposed upon each other. The focus detection areasdefined in the two methods overlap each other at the five positions. Bysetting the length of the focus detection areas defined in the imagereformation method to a value greater than that of the length of thefocus detection areas defined in the micro-lens method, a greater shiftcan be taken for the image shift calculation so as to increase thedefocus amount detection range. If the focus detection areas are set toassume a great length in the micro-lens method, a greater number offocus detection pixels is required, which is bound to lead to lowerquality in the captured image.

In addition, by defining the focus detection areas in the imagereformation method (exclusive AF) over a greater width compared to thewidth of the focus detection areas defined in the micro-lens method(image sensor AF), it is possible to ensure that the output level is notlowered even when the brightness is low and that the response does notbecome poor when the electrical charges are stored over a greater lengthof time. If the width of the focus detection areas defined in themicro-lens method is increased, it becomes necessary to increase thenumber of focus detection pixels or increase the size of the focusdetection pixels, which is bound to lower the quality of the capturedimage.

By selecting a smaller detection pitch for the focus detection areasused in the image reformation method (exclusive AF) compared to thedetection pitch selected for the focus detection areas defined in themicro-lens method (image sensor AF), the image shift amount detectionaccuracy (focus detection accuracy) can be improved. If, on the otherhand, a larger detection pitch is selected for the focus detection areascorresponding to the image reformation method, it is possible to ensurethat the output level is not lowered even when the brightness is low andthat the response is not slowed down when the charges are stored over agreater length of time. At the same time, the number of outputs can bereduced, which, in turn, makes it possible to sustain the desiredresponse level through a reduction in the length of time required forthe image shift calculation. It is more advantageous in the micro-lensmethod (image sensor AF) to match the focus detection pixel pitch withthe imaging pixel pitch and the focus detection pixels cannot easily beset to a larger pitch in the micro-lens method (image sensor AF).

The characteristics of the AF (exclusive AF) executed with the focusdetection sensor 207 through the image reformation method and thecharacteristics of the AF (image sensor AF) executed through themicro-lens method are summarized in Table 1.

TABLE 1 comparison of characteristics of exclusive AF and image sensorAF characteristics description Exclusive AF image sensor AF AF unit sizerelatively large relatively small brightness low to high intermediate todetection range high defocus amount Wide narrow detection range focusdetection inferior to image high accuracy sensor AF multi-AF area Suitednot suited control high-density AF not suited suited area settingdetection pitch larger than image fine sensor AF pinpoint detection notsuited suited interlocking with not suited suited imaging operationmoving subject Suited not suited

The AF unit for the exclusive AF, which requires the space for the imagereformation, needs to have larger dimensions than the image sensor AFunit and, in particular, it needs to have a significant thickness takenalong the optical axis. The image sensor AF unit, on the other hand,with the photoelectric conversion units disposed directly behind themicro-lenses, is allowed to assume smaller dimensions compared to theexclusive AF unit and, in particular, it is allowed to assume smallerdimensions along the optical axis. The exclusive AF unit, in which thephotoelectric conversion units are allowed to assume a considerablesize, is enabled to execute focus detection over a wide brightnessrange, from low to high brightness levels. The image sensor AF unit, onthe other hand, is embedded in the image sensor and, since thisstructure does not allow its photoelectric conversion units to assume asignificant size, the focus detection cannot be executed with ease atlow brightness levels with the image sensor AF.

Through the exclusive AF in conjunction with which the focus detectionareas assume a significant length and the gravitational centers of therange-finding pupils form a small opening angle, a large defocus amountcan be detected within its defocus amount detection range. In otherwords, the defocus amount detection range of the exclusive AF is large.In the case of the image sensor AF in conjunction with which the focusdetection areas assume a small length and the gravitational centers ofthe range-finding pupils form a large opening angle, on the other hand,the defocus amount detection range is limited. Through the exclusive AFin conjunction with which a large detection pitch is set on theestimated focus plane and the gravitational centers of the range-findingpupils form a small opening angle, the focus detection cannot beexecuted as accurately as that achieved through the image sensor AF. Inother words, through the image sensor AF in conjunction with a finedetection pitch is set on the estimated focus plane and thegravitational centers of the range-finding pupils form a large openingangle, the focus detection can be executed with a high level ofaccuracy.

In order to enable multi-AF area control (independent control on thelength of electrical charge storage period for the group ofphotoelectric conversion units corresponding to each of the plurality offocus detection positions and independent output read), the exclusive AFunit includes groups of photoelectric conversion units eachcorresponding to one of the focus detection positions and CCD registerseach used to read out the output from a specific photoelectricconversion unit group. As a result, the length of electrical chargestorage period can be controlled independently in correspondence to eachof the focus detection positions and the output from the photoelectricconversion unit group corresponding to each focus detection position canbe read out independently. In the image sensor AF unit, which includesphotoelectric conversion unit groups, each corresponding to one of thevarious focus detection positions and a read circuit, both provided aspart of the image sensor, independent electrical charge storage periodcontrol and independent output read cannot be executed as easily.

Since the exclusive AF unit needs to include an image reforming opticalsystem in correspondence to each of the focus detection positions, agreater number of focus detection positions cannot be set in closeproximity to one another with ease and thus, AF areas cannot be set witha high level of density. In the case of image sensor AF, AF areas can beset with ease each in correspondence to one of the focus detectionpositions set in close proximity to one another, simply by disposingfocus detection pixels on the image sensor surface.

Since the photoelectric conversion units in the exclusive AF unit assumea significant size so as to enable focus detection at low brightnesslevels, the detection pitch cannot be set as fine as that in the imagesensor AF unit. In the image sensor AF unit, which allows the focusdetection pixels to assume a size equal to that of the imaging pixels,the detection pitch can be set finely.

The exclusive AF and the image sensor AF are compared with regard topinpoint detection. The term “pinpoint detection” refers to focusdetection executed over a very small image portion (e.g., the eye areaof a person). The size of the photoelectric conversion units used in theexclusive AF is large, and a considerably large area is needed inconjunction with the sufficient number of photoelectric conversion unitsrequired for image shift detection. For this reason, the exclusive AF isnot suited for the pinpoint detection. The image sensor AF, on the otherhand, executed by using the small focus detection pixels, only requiresa small area in conjunction with the sufficient number of photoelectricconversion units needed for image shift detection, and thus, it issuited for the pinpoint detection.

Since the exclusive AF unit is not part of the image sensor, an offsetadjustment (mechanical or in software) for the relative positionaldifference needs to be executed when calculating the defocus amountmanifesting on the image sensor in order to allow the exclusive AF toeffectively interlock with the imaging operation. The image sensor AFexecuted by using the focus detection pixels included in the imagesensor, on the other hand, does not require any offset adjustment.

Through the exclusive AF, which allows focus detection to be executedsimultaneously over a plurality of AF areas independently of oneanother, the focus can be detected with a high level of reliability evenwhen the subject moves within the imaging plane 100 over time. The imagesensor AF, which does not facilitate simultaneous focus detection in aplurality of AF areas as readily as the exclusive AF, is not suited forfocus detection of a moving subject.

FIG. 12 presents a flowchart of the operations executed in the digitalstill camera (imaging device) shown in FIG. 1. After the power to thecamera is turned on, the body CPU 214 repeatedly executes the processingstarting in step S100. As the power to the camera is turned on andimaging operation is started in step S100, the operation proceeds tostep S110. In step S110, a focus detection operation is executed in allthe AF areas used for the exclusive AF and the data resulting from thefocus detection operation are read out. In step S120 following stepS110, image shift detection calculation processing is executed basedupon the pair of sets of image data corresponding to each of the AFareas to calculate the image shift amount in each AF area. The procedurethrough which the image shift amount is calculated is now explained inreference to the flowchart presented in FIG. 13.

In step S300 in the flowchart presented in FIG. 13, the image shiftamount detection operation is started before the operation proceeds tostep S310. In step S310, correlational shift operation calculation isexecuted on the pair of sets of data over a predetermined shift range.In step S320 following step S310, a decision is made as to whether ornot there is a minimal point in conjunction with which three-pointinterpolation calculation can be executed. If it is decided that thereis no such minimal point, the operation proceeds to step S360 in whichit is judged that image shift detection is not possible (disabled focusdetection), before the operation proceeds to step S370.

If, on the other hand, it is decided in step S320 that there is aneligible minimal point, the operation proceeds to step S330 tointerpolate the maximum correlational quantity at a point close to thecorrelation quantity indicating the highest extent of correlation. Instep S340 following step S330, the reliability of the maximumcorrelation quantity is judged. If it is decided that the maximumcorrelation quantity is not reliable, image shift detection is judged tobe not possible (disabled focus detection) in step S360 before theoperation proceeds to step S370. If, on the other hand, it is decided instep S340 that the maximum correlation quantity is reliable, theoperation proceeds to step S350 to designate the shift amountcorresponding to the calculated maximum correlation quantity as theimage shift amount and then the operation proceeds to step S370. In stepS370, the operation proceeds to step S130 in the flowchart presented inFIG. 12.

In step S130 in FIG. 12, the image shift amounts corresponding to theindividual AF areas are converted to defocus quantities. The processingexecuted to convert each image shift amount to a defocus amount is nowexplained in reference to the flowchart presented in FIG. 14. In stepS400, a defocus amount conversion operation is started and then theoperation proceeds to step S410. In step S410, a decision is made as towhether or not the image shift amount detection is disabled. If it isdecided that the image shift amount detection is disabled, the operationreturns from step S450 to the flowchart presented in FIG. 13.

If it is decided that the image shift amount detection is enabled instep S410, the operation proceeds to step S420. In step S420, the imageshift amount is multiplied by a predetermined conversion coefficient(which assumes different values in conjunction with the imagereformation method and the micro-lens method), thereby obtaining throughcalculation the defocus amount. In step S430 following step S420, adecision is made as to whether or not the image shift amount has beencalculated through the exclusive AF. If it is decided that the imageshift amount has not been calculated through the image sensor AF, theoperation returns from step S450 to the flowchart presented in FIG. 13.If, on the other hand, it is decided that the image shift amount hasbeen calculated through the exclusive AF, the operation proceeds to stepS440. In step S440, the offset amount is added to the defocus amounthaving been calculated, before the operation returns from step S450 tothe flowchart presented in FIG. 13.

The offset amount added to the defocus quantities in this processingrepresents the difference between the exclusive AF and the image sensorAF, and a value obtained in advance through measurement and stored inmemory can be used as the offset amount. Alternatively, a defocus amountobtained through focus detection executed through the image sensor AFafter achieving focus match through the exclusive AF may be used as theoffset amount.

Let us now resume the explanation in reference to the flowchartpresented in FIG. 12. In step S140, a decision is made based upon thedefocus quantities calculated in correspondence to the individual AFareas as to the specific AF area where the subject is captured. Forinstance, the object present in the closest range within the imagingplane 100 is normally most likely to be the photographic subject andaccordingly, the AF area in correspondence to which the defocus amountindicating the closest range has been calculated may be recognized asthe subject capturing area.

The image shift detection calculation processing (correlationalalgorithm) is now explained by using a specific AF area as an example.The correlation quantity C(L) is first calculated by using thedifferential correlational algorithm expressed in (1) below, with ei andfi (i=1 to m) representing the pair of sets of data corresponding to theAF area.C(L)=Σ|e(i+L)−f(i)|  (1)L in expression (1) is an integer representing the relative shift amountindicated in units corresponding to the pitch of the pair of sets ofdata. In addition, L assumes a value within a range Lmin to Lmax (−5 to+5 in the figure). The parameter i assumes a value within a range p toq, with p and q satisfying a conditional expression 1≦p≦q≦m. Thespecific values assumed for p and q define the size of the focusdetection area.

As shown in FIG. 16A, the results of the calculation executed asexpressed in (1) indicate the smallest correlation quantity C(L) incorrespondence to the shift amount L=kj (kj=2 in FIG. 16A) indicatingthe highest level of correlation between a pair of sets of data. Next, ashift amount x, which will provide the minimum value C(L)min=C(x) in acontinuous curve representing the correlation quantities is determinedthrough the three-point interpolation method as expressed in (2) to (5)below.x=kj+D/SLOP  (2)C(x)=C(kj)−|D|  (3)D={C(kj−1)−C(kj+1)}/2  (4)SLOP=MAX{C(kj+1)−C(kj), C(kj−1)−C(kj)}  (5)In addition, a defocus amount DEF representing the extent of defocusingof the subject image plane relative to the estimated focus plane can bedetermined as expressed in (6) below based upon the shift amount xhaving been calculated.DEF=KX·PY·x  (6)PY in expression (6) represents the detection pitch, whereas KX inexpression (6) represents the conversion coefficient that is determinedin correspondence to the opening angle formed at the gravitationalcenters of the pair of range-finding pupils.

The judgment as to whether or not the calculated defocus amount DEF isreliable is made as follows. As shown in FIG. 16B, the interpolatedminimum value C(X) of the correlation quantity increases when the levelof correlation between the pair of sets of data is low. Accordingly, ifC(X) is equal to or greater than a predetermined value, the defocusamount is judged to be less reliable. Alternatively, C(X) may bestandardized with regard to the data contrast, and in such a case, ifthe value obtained by dividing C(X) by SLOP indicating a value inproportion to the contrast is equal to or greater than a predeterminedvalue, the defocus amount should be judged to be not reliable. As afurther alternative, if SLOP indicating the value in proportion to thecontrast is equal to or less than a predetermined value, the subjectshould be judged to be a low contrast subject and, accordingly, thereliability of the calculated defocus amount DEF should be judged to below.

It is to be noted that if the level of correlation between the pair ofsets of data is low and the correlation quantity C(L) does not dip atall over the shift range Lmin to Lmax, as shown in FIG. 16C, the minimumvalue C(X) cannot be determined. Under such circumstances, it is judgedthat the focus detection is disabled.

FIG. 15 presents a flowchart of the operation executed in step S140 inFIG. 12 to determine the subject capturing AF area. In step S500, thesubject capturing AF area verification operation is started and then theoperation proceeds to step S510. In step S510, a decision is made as towhether or not the focus detection is disabled in all the AF areas. Ifthe focus detection is determined to be disabled in all the AF areas, adecision is made as to whether or not the image shift amount detectionis disabled, and if the image shift amount detection is judged to bedisabled, the proceeds to step S530. In step S530, the central AF area(the AF area set at the center of the imaging plane 100) is designatedas a temporary subject capturing AF area for convenience, and then theoperation returns to the flowchart presented in FIG. 12 from step S540.

If, on the other hand, it is decided that the focus detection is enabledin step S510, the operation proceeds to step S520. If it is decided thatthere is at least one AF area, the AF area, in correspondence to whichthe defocus amount indicating the closest range has been calculated, isrecognized as the subject capturing AF area in step S520, before theoperation returns from step S540 to the flowchart presented in FIG. 12.

In step S150 in the flowchart presented in FIG. 12, a decision is madeas to whether or not the absolute value of the defocus amount havingbeen calculated in correspondence to the subject capturing AF area isequal to or less than a predetermined value. The predetermined value isselected in advance to be used to judge whether or not the subject isalmost in focus through the exclusive AF. If the absolute value of thedefocus amount calculated in correspondence to the subject capturing AFarea is equal to or less than the predetermined value, it is judged tobe already almost in focus. It is to be noted that if the focusdetection is disabled (disabled image shift detection) in all the AFareas, the operation proceeds to step S170. In addition, if it is judgedthat the current status does not indicate a near focus match condition,the operation proceeds to step S160. In step S160, the defocus amount istransmitted to the lens drive control circuit 206 so as to enable thelens drive control circuit to drive the focusing lens 210 in theexchangeable lens 202 to the focus match position. Once the processingin step S160 ends, the operation returns to step S110 to repeatedlyexecute the operations described above.

If, on the other hand, it is decided that the current status indicates anear focus match condition, the operation proceeds to step S170. In stepS170, a decision is made as to whether or not a shutter release has beenexecuted. If it is decided that a shutter release has not been executed,the operation returns to step S110 to repeatedly execute the operationsdescribed above. If it is decided that a shutter release has beenexecuted, the operation proceeds to step S180 to read out data from thefocus detection pixels in the image sensor AF unit corresponding to theverified subject capturing AF area. In step S190 following step S180,the image shift detection calculation processing is executed based uponthe pair of sets of image data corresponding to the subject capturing AFarea to determine the image shift amount.

In step S200 following step S190, the image shift amount having beencalculated in correspondence to the subject capturing AF area isconverted to the defocus amount. In step S210, following step S200, adecision is made as to whether or not the absolute value of the defocusamount calculated for the subject capturing AF area is equal to or lessthan a predetermined value. The predetermined value is selected to beused when making a decision as to whether or not a focus match has beenachieved through the image sensor AF (a value smaller than thepredetermined value, which is used when making a decision as to whetheror not a predetermined level of near focus match has been achieved inthe exclusive AF, should be selected). If the absolute value of thedefocus amount calculated for the subject capturing AF area is equal toor less than the predetermined value, it is judged that a focus matchhas been achieved in the subject capturing AF area, before the operationproceeds to step S230. It is to be noted that if the focus detection isnot possible (disabled image shift detection) in any of the subjectcapturing AF areas, the operation proceeds to step S230.

If it is decided that a focus match has not been achieved, the operationproceeds to step S220. In step S220, the defocus amount is transmittedto the lens drive control circuit 206 to enable the lens drive controlcircuit to drive the focusing lens 210 in the exchangeable lens 202 tothe focus match position and then the operation proceeds to step S230.In step S230, image signals are read out from the imaging pixels at theimage sensor, before the operation proceeds to step S240. In step S240,the image signals are saved into the memory card 219, before theoperation returns to step S110 to repeatedly execute the operationsdescribed above.

Table 2 presents examples of positional arrangements that may be adoptedin the digital camera for the focus detection sensor (exclusive AF) thatexecutes focus detection through the image reformation method and forthe image sensor (image sensor AF) that executes focus detection throughthe micro-lens method, in a format that facilitates comparison.

TABLE 2 positional arrangement examples for exclusive AF unit and imagesensor AF unit and features of individual examples positionalarrangement examples features (1) A fixed half mirror The mirror doesnot need to disposed in the light path of retreat, and thus high theimaging optical system, response is assured. with the image sensor AFunit Since reflected light is disposed on the reflection received at theimage sensor side of the fixed half mirror AF unit, the image quality isand the exclusive AF unit not compromised. disposed on the transmissionAF operation can be executed side of the fixed half mirror. via theexclusive AF unit concurrently while photographing operation is inprogress (2) A fixed half mirror The mirror does not need to disposed inthe light path of retreat, and thus high the imaging optical system,response is assured. with the image sensor AF unit The camera body canassume disposed on the transmission a low profile along the side of thefixed half mirror optical axis. and the exclusive AF unit AF operationcan be executed disposed on the reflection via the exclusive AF unitside of the fixed half mirror. concurrently while photographingoperation is in progress. (3) A movable total Since no mirror is presentin reflection mirror disposed the light path during imaging in the lightpath of the operation, a high image imaging optical system, with qualityis assured. the exclusive AF unit Since the light flux is not disposedon the reflection split, better detection side of the movable totalcapability is assured at low reflection mirror and the brightnesslevels. image sensor AF unit disposed at the image forming positionwhere the image is formed in the imaging optical system while themovable mirror is in a off-path state. (4) An exclusive AF unit Themirror does not need to (outside light AF unit) retreat, and thus highprovided separately from the response is assured imaging optical systemand an Since no mirror is present image sensor AF unit disposed in thelight path during at the image forming position imaging operation, ahigh at which the image is formed image quality is assured. via theimaging optical Since the light flux is not system. split, betterdetection capability is assured at low brightness levels. AF operationcan be executed via the exclusive AF unit concurrently whilephotographing operation is in progress.

The positional arrangement shown in FIG. 1 is summarized as positionalarrangement example (1). In this example, a fixed half mirror isdisposed in the light path of the imaging optical system, the imagesensor AF unit is disposed on the reflection side of the half mirror,and the exclusive AF unit is disposed on the transmission side of thehalf mirror. The positional example is characterized in that since thehalf mirror is fixed, it does not need to retreat when capturing animage. This means that the imaging operation can be executed with aminimum release time lag. In addition, since the image is captured atthe image sensor by using the light reflected at the half mirror insteadof the light transmitted through the glass constituting the half mirror,the quality of the image is not lowered. Furthermore, the exclusive AFunit can be engaged in operation to execute focus adjustmentconcurrently while an imaging operation is in progress at the imagesensor.

The positional arrangement shown in FIG. 18 is summarized as positionalarrangement example (2). In this example, a fixed half mirror isdisposed in the light path of the imaging optical system, with theexclusive AF unit disposed on the reflection side of the half mirror andthe image sensor AF unit disposed on the transmission side of the halfmirror. Namely, the positions of the exclusive AF unit and the imagesensor AF are reversed from those in positional arrangement example (1).

An explanation is given in reference to FIG. 18 with the same referencenumerals assigned to components identical to those shown in FIG. 1. Thepositional arrangement in FIG. 18 is characterized in that the fixedhalf mirror does not need to retreat when capturing an image and thus,the imaging operation can be executed with a minimum release time lag.In addition, since the image sensor is disposed along the optical axis,the camera body 203 is allowed to assume a smaller thickness measuredalong the optical axis, which in turn, makes it possible to provide acompact camera body 203. Furthermore, the exclusive AF unit can beengaged in operation to execute focus adjustment concurrently while animaging operation is in progress at the image sensor.

The positional arrangement shown in FIG. 19 is summarized as positionalarrangement example (3). In this example, a main mirror 230 (movablehalf mirror) is disposed in the light path of the imaging optical systemand reflected light is guided to an optical viewfinder disposed in thelight path on the reflection side and constituted with a pentaprism 232and the eyepiece lens 217. The explanation provided below focuses on thedifferences with the same reference numerals assigned to components inFIG. 19 identical to those shown in FIG. 1 so as to eliminate a repeatedexplanation thereof.

A light flux having been transmitted through the main mirror 230 isreflected at a sub mirror 231 (movable total reflection mirror) disposedto the rear of the main mirror, the reflected light is then guided tothe focus detection exclusive sensor 207 used exclusively for focusdetection positioned outside the imaging light path, and focus detectionis executed at the focus detection exclusive sensor 207. In response toan imaging instruction, the main mirror 230 and the sub mirror 231retreat from the imaging light path to allow the image sensor to receivethe light flux, thereby enabling focus detection and imaging operationat the image sensor. This positional arrangement example ischaracterized in that since the mirrors retreat from the imaging lightpath when capturing an image to allow the image sensor to directlyreceive the imaging light flux, a high quality image can be obtained. Inaddition, since the light flux is not divided into a light flux for theexclusive AF and for the image sensor AF, the structure assures asufficient light quantity with better ease even when the brightness islow.

The positional arrangement shown in FIG. 20 is summarized as positionalarrangement example (4). In this example, a range-finding device 240that uses outside light (e.g., a reflected light receiving active AFunit, an image shift detection-type passive AF unit or an active AF unitadopting the “time of flight” method that utilizes ultrasound waves orlight waves) is utilized as the exclusive AF unit. An explanation is nowgiven in reference to FIG. 20, with the same reference numerals assignedto components identical to those shown in FIG. 1. The image sensor AFunit 212 receives the light flux from the exchangeable lens 202 at alltimes.

In the structure shown in FIG. 20, focus adjustment is executed byengaging the exclusive AF unit in operation prior to a shutter releaseand once a shutter release occurs, an image is captured after executinga focus adjustment via the image sensor AF unit. This makes it possibleto execute focus detection even when the brightness is low, whendefocusing manifests to a large extent or when the focus detection needsto be executed over multiple AF areas. At the same time, the structureassures a highly accurate focus match during an imaging operation. Thispositional arrangement example is characterized in that since thestructure does not require the half mirror to retreat when capturing animage, the imaging operation can be executed with a minimum shutterrelease time lag. In addition, a high-quality image can be obtained withthe imaging light flux directly received at the image sensor without anyredundant optical elements disposed in the imaging light path.Furthermore, since the light flux does not need to be split, asufficient quantity of light can be secured even when the brightness islow. Also, the exclusive AF unit can be engaged in operation to executefocus adjustment concurrently while an imaging operation is in progressat the image sensor.

Table 3 provides a list of specification for the exclusive AF unit andthe image sensor AF, adopting a format that facilitates comparison.

TABLE 3 specification settings for exclusive AF and image sensor AFspecification description exclusive AF image sensor AF range-findinglarge small pupil distance (1) range-finding matched matched pupildistance (2) range-finding dark bright pupil f-number (1) range-findingmatched matched pupil f-number (2) range-finding bright dark pupilf-number (3) range-finding small large pupil gravitational centerinterval (1) range-finding matched matched pupil gravitational centerinterval (2) AF area positions matched matched (1) AF area positionsvaried varied (2) AF area quantity matched matched (1) AF area quantitylarge small (2) detectionpitch (1) large (large) fine (small) detectionpitch 2 matched matched AF area length (1) large small AF area length(2) matched matched AF area width (1) large small AF area width (2)matched matched color separation not included not included filters (1)color separation not included included filters (2) infrared clip matchedmatched wavelength (1) infrared clip matched to adjusted in wavelength(2) auxiliary light correspondence to wavelength imaging pixelcharacteristicsBy selecting the optimal settings for the individual specificationcategories with the statuses of use of the exclusive AF unit (imagereformation method) and the image sensor AF unit (micro-lens Method)taken into consideration, focus adjustment achieving good overallbalance can be executed.

With regard to the “range-finding pupil distance (1)”, the exit pupildistance of a lens with a long focus, which tends to manifest a greatdefocus amount under normal circumstances, is large. Since the eclipseof the focus detection light fluxes can be prevented more effectively bymatching the exit pupil distance of the exchangeable lens with therange-finding pupil distance, a large range-finding pupil distance isselected for the exclusive AF unit so as to give priority to thedetection of defocusing occurring to a large extent. The range-findingpupil distance is set to a small value for the image sensor AF unit soas to enable focus detection for a lens with a short focus which tendsto manifest defocusing to a lesser extent. With regard to the“range-finding pupil distance (2)”, a higher level of uniformity can beassured for the extent to which the difference between the range-findingpupil distance set for the exclusive AF unit and the range-finding pupildistance set for the image sensor AF affects the focus detection results(the extent to which the focus detection accuracy is adversely effectedby the eclipse of the focus detection light fluxes) by matching therange-finding pupil distances selected for the exclusive AF unit and theimage sensor AF unit with each other. By matching the range-findingpupil distances, similar results are obtained regardless of which AFunit adopting one of the two different methods is used.

With regard to the “range-finding pupil f-number (1)”, the range-findingpupil f-number is raised for the exclusive AF unit to achieve a darkersetting so as to enable focus detection for a dark lens with a largeminimum f-number and enable detection of defocusing manifesting to alarge extent. A smaller range-finding pupil f-number is selected for theimage sensor AF unit for a brighter setting to enable highly accuratefocus detection for a light lens with a small minimum f-number andoptimize the image sensor AF unit for detection of defocusingmanifesting only to a small extent near the focus match point.

In addition, with regard to the “range-finding pupil f-number (2)”, ahigher level of uniformity can be assured for the extent to which thedifference between the range-finding pupil minimum f-numbers selectedfor the exclusive AF unit and the image sensor AF affects the focusdetection results (the extent to which the focus detection accuracy isadversely affected by the eclipse of the focus detection light fluxes)by selecting matching range-finding pupil f-numbers for the exclusive AFunit and the image sensor AF unit, when the distance from the opticalaxis of the exchangeable lens 202 to the focus detection positions usedfor the exclusive AF and the distance from the optical axis of theexchangeable lens 202 to the focus detection positions used for theimage sensor AF are equal to each other in the imaging plane 100. Byselecting such matching range-finding pupil f-numbers, similar resultscan be obtained regardless of which AF unit adopting one of the twodifferent methods is utilized.

With regard to the “range-finding pupil f-number (3)”, a smallrange-finding pupil f-number is selected for the exclusive AF unit for abrighter setting so as to improve the detection capability at lowbrightness levels. A larger range-finding pupil f-number is selected forthe image sensor AF unit for a darker setting so as to optimize theimage sensor AF for the focus detection executed at extremely highbrightness levels (optimize the image sensor AF for control executed inconjunction with an extremely short charge storage period).

With regard to the “range-finding pupil gravitational center interval(1)”, the range-finding pupil gravitational center interval (openingangle) is set to a small value for the exclusive AF unit so as to enabledetection of defocusing occurring to a large extent, whereas a largerange-finding pupil gravitational center interval (opening angle) isselected for the image sensor AF unit so as to assure a highly accuratefocus detection near the focus match point. In addition, with regard tothe “range-finding pupil gravitational center interval (2)”, a higherlevel of uniformity is assured for the extent to which the differencebetween the range-finding pupil gravitational center intervals (openingangles) affects the focus detection results, by matching therange-finding pupil gravitational center interval (opening angle) forthe exclusive AF unit with the range-finding pupil gravitational centerinterval (opening angle) for the image sensor AF unit. This, in turn,assures similar results to be obtained regardless of which AF unitadopting one of the two different methods is utilized.

With regard to the “AF area positions (1)”, the AF areas are set atmatching positions for the exclusive AF and the image sensor AF so as toallow either of the two different methods, better suited to the currentconditions, to be selected when executing focus detection over the sameAF areas. With regard to the “AF area positions (2)”, the AF areas forthe exclusive AF and the AF areas for the image sensor AF are set atpositions different from each other to provide a greater number of AFareas within the imaging plane 100. For instance, AF areas may be setdensely around the center of the imaging plane 100 in correspondence tothe image sensor AF unit and AF areas may be set more sparsely over theperiphery of the imaging plane 100 in correspondence to the exclusive AFunit.

With regard to the “AF area quantity (1)”, the AF areas for theexclusive AF and the AF areas for the image sensor AF are set atmatching positions in matching quantities so as to allow either of thetwo different methods, better suited to the current conditions, to beselected for all the AF areas. With regard to the “AF area quantity(2)”, a greater number of AF areas is set in correspondence to theexclusive AF so as to dedicate the exclusive AF unit for focus detectionin multiple AF areas, whereas a smaller number of AF areas is set inconjunction with the image sensor AF so as to dedicate the image sensorAF unit to high accuracy focus detection in a single AF area.

With regard to the “detection pitch (1)”, a larger detection pitch(sampling pitch) is selected for the exclusive AF so as to ensure thatthe number of sets of data does not increase even when the AF areasassume a significant length to enable detection of defocusing occurringto a great extent, which, in turn, prevents an increase in the length oftime required for the arithmetic operation and thus prevents theresponse from becoming poorer. For the image sensor AF, on the otherhand, a fine detection pitch is selected so as to enable highly accurateimage shift detection. With regard to the “detection pitch (2)”,matching detection pitches are selected for the exclusive AF and theimage sensor AF so as to assure a higher level of uniformity for theextent to which the difference between the detection pitches affects thefocus detection results (an error in the image shift detection, theselectability of the subject pattern and the like). This, in turn,assures similar results to be obtained regardless of which AF unit,adopting one of the two different methods, is utilized.

With regard to the “AF area length (1)”, the AF areas set in conjunctionwith the exclusive AF assume a greater length so as to assure asufficient image shift range for the detection of defocusing manifestingto a great extent and also assure a higher level of reliability incapturing the subject. The AF areas set in conjunction with the imagesensor AF, on the other hand, assume a smaller length so as to optimizethe image sensor AF for focus detection near the focus match point wherethe image shift manifests only to a small extent and also to enablepinpoint focus detection. With regard to the “AF area length (2)”, theAF areas set in conjunction with the exclusive AF and the image sensorAF assume matching lengths so as to achieve a higher level of uniformityfor the extent to which the difference between the AF area lengthsaffects the focus detection results (an error in the image shiftdetection, the selectability of the subject pattern and the like). This,in turn, assures similar results to be obtained regardless of which AFunit, adopting one of the two different methods, is utilized.

With regard to the “AF area width (1)”, a greater AF area width isselected for the exclusive AF to assure a sufficient quantity of lighteven when the brightness is low, whereas a smaller AF area width isselected for the image sensor AF to enable detection of a finer subjectpattern. With regard to the “AF area width (2)”, the AF areascorresponding to the exclusive AF and the AF areas corresponding to theimage sensor AF assume matching widths so as to assure a higher level ofuniformity for the extent to which the AF area width difference affectsthe focus detection results (an error in the image shift detection, theselectability of the subject pattern and the like). This, in turn,assures similar results to be obtained regardless of which AF unit,adopting one of the two different methods, is utilized.

With regard to the “color separation filters (1)”, no color separationfilters are used either in conjunction with the exclusive AF or inconjunction with the image sensor AF, so as to eliminate any effect thatcolor separation filters might have on the focus detection results (theselectability of the subject pattern and the like). This, in turn,assures similar results to be obtained regardless of which AF unit,adopting one of the two different methods, is utilized.

With regard to the “color separation filters (2)”, no color separationfilters (R, G and B color filters) are disposed at the photoelectricconversion units in the exclusive AF unit in order to assure asufficient quantity of light even when the brightness is low. Colorseparation filters are, however, disposed at the focus detection pixelsin the image sensor AF unit so as to improve the image quality by usingthe outputs from the focus detection pixels equipped with the colorfilters as well when interpolating image signals at the focus detectionpixel positions with the outputs from the surrounding imaging pixels andalso to enable focus detection for a subject that manifests a change inhue but does not manifest any change in brightness by executing thefocus detection in correspondence to each color.

With regard to the “infrared clip wavelength (1)”, the infrared clippingfilters installed on the entry sides of the exclusive AF unit and theimage sensor AF unit are both set to clip the infrared light withmatching wavelengths, so as to eliminate the effect (infraredaberration) of the infrared component contained in the light fluxtraveling from the subject on the focus detection results. This, inturn, assures similar results to be obtained regardless of which AFunit, adopting one of the two different methods, is utilized.

With regard to the “infrared clip wavelength (2)”, the infrared clipwavelength for the infrared clipping filter installed on the entry sideof the exclusive AF unit is set so as to clip light containing AFauxiliary light and thus assure a desired level of focus detectionperformance even when the brightness is low. The infrared clipwavelength for the infrared clipping filter installed on the entry sideof the image sensor AF unit, on the other hand, is set in correspondenceto the infrared clipping characteristics of the imaging pixels so as toprevent an error attributable to the infrared aberration and to allowthe outputs from the focus detection pixels to be used as image signalsas well. It is to be noted that the term “AF auxiliary light” refers tolight radiated onto the subject to increase the quantity of light whenthe brightness is low, and light with a large wavelength (red toinfrared) with significant light emission energy is used as the AFauxiliary light.

FIG. 17 presents a flowchart of the focus detection operation. In theflowchart presented in FIG. 12, the exclusive AF unit is engaged inoperation for large focus adjustment and the image sensor AF unit isengaged in operation for fine focus adjustment. The procedure of thefocus detection is now explained in reference to the flowchart presentedin FIG. 17.

After the power is turned on in step S900, the operation proceeds tostep S910. In step S910, a decision is made with regard to whether theexclusive AF or the image sensor AF should be selected in correspondenceto the current conditions. If it is decided that the exclusive AF unitis to be utilized, the operation proceeds to step S920 to execute focusadjustment via the exclusive AF unit, before the operation returns tostep S910. If, on the other hand, it is decided in step S910 that theimage sensor AF unit is to be utilized, the operation proceeds to stepS930 to execute focus adjustment via the image sensor AF unit, beforethe operation returns to step S910.

The decision with regard to the AF selection is made in step S910 so asto optimize the overall focus adjustment operation in the imagingdevice. Namely, the decision is made so as to select either theexclusive AF or the image sensor AF to take full advantage of thestrengths of the image reformation method and the micro-lens methodadopted in conjunction with the exclusive AF and the image sensor AF.For instance, the switch-over should be executed based upon the judgingcriteria (judging conditions) presented in Table 4.

TABLE 4 switch-over judging for switching to exclusive AF or imagesensor AF judging criteria exclusive AF image sensor AF shutter releaseshutter release shutter release instruction instruction not instructionissued issued defocus amount large small continuous continuous singleimage shooting/single shooting in shooting in image shooting (1)progress progress continuous single image continuous shooting/singleshooting in shooting in image shooting (2) progress progress movieshooting/ movie shooting still image still image shooting shooting (1)movie shooting/ still image movie shooting still image shooting shooting(2) brightness low high moving/stationary moving subject stationarysubject photographic subject AF area mode multiple AF areas single AFarea AF area positions periphery center (1) AF area positions arbitrarysetting arbitrary setting (2) AF mode continuous AF one-shot AF use ofauxiliary auxiliary light auxiliary light light used not used AF/MF AFMF display display in reduced display in size enlarged size lens minimumdark bright f-number lens focal length large small control f-number darkbright shutter speed high low sensitivity high low setting strobe strobenon-strobe photographing photographing photographing operation operationself timer non-self timer self timer photographing photographingphotographing operation operation hand-held/fixed hand-held fixedphotographing photographing photographing photographing mode sports modeportrait modeBy switching from the exclusive AF (image reformation method) to theimage sensor AF (micro-lens method) and vice versa in an optimal mannerwith the conditions under which the imaging device is currently utilizedtaken into consideration, focus adjustment achieving a good overallbalance can be executed.

With regard to the “shutter release (imaging command) yes/no criterion”,the exclusive AF is selected before a shutter release operation isperformed at the shutter button, since the following requirements shouldbe satisfied prior to the shutter release operation.

-   (1) Focus adjustment must be executed for a subject that has become    significantly blurred due to a change in the image composition or    the like.-   (2) Focus adjustment should be executed for an object most likely to    be the photographic subject when a plurality of objects are present    within the imaging plane 100.-   (3) Focus adjustment should be executed by giving priority to good    response rather than accuracy.-   (4) Focus adjustment should be enabled even when the brightness is    low.    After the shutter release operation is performed at the shutter    button, however, it becomes more important to achieve a highly    accurate focus adjustment immediately before capturing the image    and, accordingly, the image sensor AF unit is engaged

—Defocus Quantity—

When defocusing manifests to a great extent, the exclusive AF unitcapable of detecting a large defocus amount is engaged in operation toexecute the focus adjustment by driving the lens to a point near thefocus match position. As the lens is driven to the point near the focusmatch position and thus the extent of defocusing becomes reduced, theimage sensor AF unit capable of highly accurate focus adjustment isselected.

—Continuous Shooting and Single Image Shooting (1)—

When the imaging device is engaged in a continuous shooting (duringwhich images are captured successively with short intervals), it islikely that the subject is moving and, accordingly, the exclusive AFunit capable of high-response focus adjustment for a moving subject isengaged. During a single image photographing operation (during which asingle image is captured in response to a single shutter releaseoperation), the photographic subject is likely to be stationary and, forthis reason, the image sensor AF unit capable of highly accurate focusadjustment for a stationary photographic subject is engaged.

—Continuous Shooting and Single Image Shooting (2)—

When the system represented by example (3) in Table 2 is utilized,engagement of the exclusive AF unit necessitates the mirror to enter thelight path and retreat from the light path to enable the focus detectionoperation and the imaging operation respectively, which disallowshigh-speed continuous shooting operation. Accordingly, the image sensorAF unit, which does not require any displacement of the mirror for thefocus detection or the imaging operation, is used for the continuousshooting operation, whereas the exclusive AF unit, more effective infocus detection executed at low brightness or in detection of defocusingoccurring to a large extent, is engaged for single image photographingoperation.

—Movie Shooting and Still Image Shooting (1)—

When the imaging device is engaged in a movie shooting (videophotographing) operation or when the imaging device is set in a movieshooting mode, the object being photographed is likely to be moving.Accordingly, the exclusive AF unit capable of high-response focusadjustment for a moving subject is engaged in operation. When theimaging device is currently engaged in a still image shooting operation(still photographing operation) or if the imaging device is currentlyset in the still shooting mode, the object being photographed is likelyto be still and, accordingly, the image sensor AF unit capable of highlyaccurate focus detection for a still photographic subject is engaged.

—Movie Shooting and Still Image Shooting (2)—

When the system represented by example (3) in Table 2 is utilized,engagement of the exclusive AF unit necessitates the mirror to enter thelight path and retreat from the light path to enable the focus detectionoperation and the imaging operation respectively, and thus, movieshooting cannot be executed. Accordingly, the image sensor AF unit,which does not require any displacement of the mirror, is used for movieshooting (video photographing) or when the imaging device is set in amovie shooting mode. While a still image shooting (still photographing)is in progress or when the imaging device is set in the still shootingmode, on the other hand, the exclusive AF unit, more effective in focusadjustment at low brightness levels or in detection of defocusingoccurring to a large extent, is engaged.

—Brightness—

When the brightness in the photographic field is lower than apredetermined value, the exclusive AF unit, more effective in focusadjustment executed at low brightness levels, is engaged in operation,whereas when the brightness level is higher than the predeterminedvalue, the image sensor AF unit capable of highly accurate focusadjustment is engaged in operation. It is to be noted that thebrightness in the photographic field is determined through an arithmeticoperation executed by the CPU 214 based upon the output from the imagesensor 212. Alternatively, the brightness in the photographic field maybe detected via a dedicated photometering element and a dedicatedphotometering circuit specifically installed for such purposes.

—Moving Photographic Subject or Stationary Photographic Subject—

Based upon any change discerned in the focus detection results (defocusamount) over time, the subject can be judged to be moving or in astationary state. If the photographic subject is judged to be moving,the exclusive AF unit capable of high-response focus adjustment for amoving photographic subject is engaged in operation. If, on the otherhand, the subject is judged to be stationary, the image sensor AF unitcapable of highly accurate focus adjustment for a stationaryphotographic subject is engaged.

—AF Area Mode—

If a multi-AF area mode for executing focus detection simultaneously ata plurality of focus detection positions has been selected via an AFarea mode selection operation member (not shown), the exclusive AF unitwith which focus detection can be executed with ease simultaneously at aplurality of focus detection positions and high-response focusadjustment can be executed is engaged in operation. If, on the otherhand, a single AF area mode for executing focus detection at a singlefocus detection position has been selected, the image sensor AF unitcapable of highly accurate focus adjustment is engaged in operation.

—AF Area Positions (1)—

When the AF areas set in the periphery of the imaging plane 100 areselected, an image with a very high image quality is not likely to beobtained over the image plane periphery due to the aberration of thelens. Accordingly, the exclusive AF unit is selected under suchcircumstances by giving higher priority to the response rather than thefocus adjustment accuracy. If, on the other hand, an AF area set at thecenter of the image plane has been selected, the image sensor AF unitcapable of highly accurate focus adjustment is selected so as tomaximize the image quality.

—AF Area Positions (2)—

When the AF areas used for the exclusive AF and the AF areas used forthe image sensor AF are set at different positions, the AF operation isexecuted through the AF method (the exclusive AF or the image sensor AF)adopted in the AF area present at a position closest to the positionwithin the imaging plane 100 specified by the user.

—AF Mode—

If a continuous AF mode for continuously executing the focus adjustmentoperation after the imaging optical system is in focus has been selectedvia an AF mode selecting operation member (not shown) so as to sustainthe focus match on a moving subject, the exclusive AF unit is engaged,since the exclusive AF unit has a high level of focus adjustmentperformance in conjunction with a moving photographic subject and isalso capable of high-response focus adjustment. If, on the other hand, aone-shot AF mode for executing stable and reliable focus detection for astationary photographic subject has been selected by locking the focusadjustment operation once the imaging optical system is in focus, theimage sensor AF unit capable of highly accurate focus adjustment isengaged.

—Use of AF Auxiliary Light—

When the brightness is low and focus detection needs to be executed byradiating AF auxiliary light on to the subject, the exclusive AF unit,more effective in the focus adjustment at low brightness levels isengaged in operation. If, on the other hand, the focus detection can beexecuted without having to radiate any AF auxiliary light, the imagesensor AF unit capable of highly accurate focus adjustment is engaged.

—AF and MF—

If an AF mode (autofocus) for automatically adjusting the focus bydriving the lens based upon the focus detection results has beenselected, the exclusive AF unit capable of high-response focusadjustment for moving photographic subjects is engaged in operation. If,on the other hand, an MF mode (manual focus; auto focus disallowed) forindicating the focus condition based upon the focus detection resultsprovided by the exclusive AF unit to allow the user to manually adjustthe focus of the lens in correspondence to the indicated focus conditionhas been selected, the image sensor AF unit capable of highly accuratefocus detection over the critical range is engaged in operation.

—Display—

If a magnification factor for an image display in a reduced size hasbeen selected when displaying an image on the electronic viewfinderconcurrently while the focus adjustment operation is in progress (in anyof the systems corresponding to examples 1, 2 and 4 in Table 2), theexclusive AF unit is engaged in operation so as to give higher priorityto better response in the focus adjustment operation. If, on the otherhand, a magnification factor for an image display in an enlarged sizehas been selected, the image sensor AF unit is engaged so as to givehigher priority to the focus matching accuracy. It is to be noted thatan operation member via which a specific image display magnificationfactor can be selected should be included in the system so as to allowthe user to select a display magnification factor for an image displayin an enlarged size or in a reduced size.

—Minimum f-number—

If the minimum f-number (maximum aperture) of the exchangeable lensmounted at the imaging device indicates a low brightness level, theexclusive AF unit which the darker range-finding pupil f-number isengaged in operation in order to ensure that the focus detectionaccuracy is not lowered due to an eclipse of the focus detection lightflux. If, on the other hand, the minimum f-number of the exchangeablelens mounted on the imaging device indicates a high light level, theimage sensor AF unit with the light range-finding pupil f-number, whichis capable of executing highly accurate focus detection, is engaged inoperation. It is to be noted that information indicating the apertureminimum f-number of the exchangeable lens and the like is transmittedfrom the lens drive control circuit 206 to the body CPU 214.

—Lens Focal Length—

If the exchangeable lens mounted at the imaging device has a large focallength, the exclusive AF unit with a large range-finding pupil distance,which is capable of detecting the defocus amount over a wide range, isengaged in operation. If, on the other hand, the exchangeable lensmounted on the imaging device has a small focal length, the image sensorAF unit with a small range-finding pupil distance, which is capable ofexecuting focus detection with high accuracy, is engaged in operation.It is to be noted that information indicating the focal length of theexchangeable lens and the like is transmitted from the lens drivecontrol circuit 206 to the body CPU 214.

—Aperture Control F Value of the Exchangeable Lens—

If a large aperture f-number (control f-number) is to be used during theimaging operation, the focal depth is significant and thus, it is notnecessary to assure a high level of focus adjustment accuracy. For thisreason, the exclusive AF unit is engaged so as to give higher priorityto better response in the focus adjustment operation. If, on the otherhand, a small control f-number is obtained, the focus detection needs tobe executed with a high level of accuracy and, for this reason, theimage sensor AF unit is engaged. It is to be noted that the aperturecontrol f-number in the exchangeable lens is determined through exposurecontrol calculation executed in the body CPU 214.

—Shutter Speed—

When a high shutter speed (short exposure time) is set for the imagingoperation, the photographic field is bound to be dark, and accordingly,the exclusive AF unit is engaged in order to assure good response in thefocus adjustment operation. When a low shutter speed (long exposuretime) is set for the imaging operation, the image sensor AF unit isengaged in operation so as to give higher priority to the focusadjustment accuracy. It is to be noted that the shutter speed isdetermined through the exposure control calculation executed in the CPU214.

—Sensitivity—

When a high sensitivity level (a high amplification factor for theoutputs from the imaging pixels at the image sensor) is selected for theimaging operation, the photographic field is bound to be dark and,accordingly, the exclusive AF unit is engaged in order to assure goodresponse in the focus adjustment operation. When a low sensitivity levelis selected for the imaging operation, the image sensor AF unit isengaged in operation so as to give higher priority to the focusadjustment accuracy. It is to be noted that the sensitivity is selectedvia a sensitivity setting operation member (not shown) and theamplification factor corresponding to the sensitivity having been set isselected for the outputs from the imaging pixels at the image sensor.

—Use of Strobe (Subject Illumination)—

The exclusive AF unit, more effective in focus adjustment at lowbrightness levels, is engaged for strobe photographing operation duringwhich an image of the subject is captured by radiating illuminatinglight onto the subject. However, when capturing an image withoutradiating illuminating light, the image sensor AF unit capable of highlyaccurate focus adjustment is engaged. In addition, if the strobephotographing operation is disallowed via a strobe photographingselection member used to select either the allow setting or the disallowsetting for strobe photographing operation, the image sensor AF unit isutilized, whereas if the strobe photographing operation is allowed viathe strobe photographing selection member, the exclusive AF unit isutilized.

—Self Timer Photographing—

When a self timer photographing mode for executing an imaging operationby first allowing a predetermined length of time to elapse afterreceiving an imaging instruction has been selected via a photographingmode selecting operation member (not shown), the photographic subject islikely to be a stationary subject, and accordingly, the image sensor AFunit capable of highly accurate focus adjustment is engaged. If, on theother hand, the self timer photographing mode has not been selected, thephotographic subject is more likely to be a moving photographic subject,and accordingly, the exclusive AF unit more suited to focus adjustmentfor moving subjects is engaged.

—Hand-held Photographing or Fixed Photographing—

For a fixed photographing operation performed by using a tripod or thelike, the photographic subject is likely to be a stationary subject,and, accordingly, the image sensor AF unit capable of highly accuratefocus adjustment is engaged. The likelihood of the photographic subjectof a hand-held photographing operation performed by holding the cameraby hand being a moving subject is higher, and accordingly, the exclusiveAF unit, more suited to focus adjustment for moving subjects, is engagedin conjunction with the hand-held photographing operation. It is to benoted that the decision as to whether or not the imaging device is in afixed state can be made by detecting whether or not the camera ismounted on a tripod or based upon the output from an angular speedsensor or an acceleration sensor built into the imaging device.

—Photographing Mode—

The user is able to select a set of photographic conditions (theaperture value, the shutter speed and the sensitivity) for the imagingoperation by selecting a specific photographing mode in correspondenceto the photographic subject. For instance, if a sports mode suited tocapturing an image of a moving photographic subject has been selectedvia the photographing mode selecting operation member (not shown), theexclusive AF unit ideal for focus adjustment for moving photographicsubjects is engaged. If, on the other hand, a portrait mode suited tocapturing an image of a stationary photographic subject has beenselected, the image sensor AF unit capable of highly accurate focusadjustment is engaged.

Table 5 is a list of AF algorithm parameter settings at the exclusive AFunit and image sensor AF unit, presented in a format that facilitatescomparison.

TABLE 5 AF algorithm parameter settings for exclusive AF and imagesensor AF characteristics description exclusive AF image sensor AFdefocus amount large small detection range disabled detection lessrigorous more rigorous threshold value focus match wide narrowrecognition range focus match area automatic judgment sustain judgmentresults provided via exclusive AF offset amount difference N/A relativeto image sensor AF

While the same image shift detection algorithm (expressions (1) to (6)and the like) is used in conjunction with the exclusive AF and the imagesensor AF, the level of the focus adjustment operation performance forthe overall imaging device can be improved by selecting the optimalparameter settings.

—Defocus Quantity Detection Range—

The defocus amount detection range is determined based upon the imageshift limits (p, q) indicated in expression (1). In conjunction with theexclusive AF, a smaller value is assumed for p and a larger value isassumed for q so as to enable detection over a wider range. Since theimage sensor AF unit is engaged in focus adjustment in the range aroundthe focus match point, a larger value is assumed for p and a smallervalue is assumed for q to narrow the image shift range and, since thisreduces the detection range, the length of time required for thearithmetic operation is reduced.

—Disabled Image Offset Detection Decision-Making Threshold Value—

The focus detection is judged to be unreliable if the minimumcorrelation quantity C(x) expressed in (3) is equal to or greater than athreshold value. This threshold value is set to assume specific valuesso that more rigorous judging criteria are applied in the image sensorAF than for the exclusive AF. Namely, the threshold value assumes agreater value in conjunction with the exclusive AF than the valueselected in conjunction with the image sensor AF. By selecting suchvalues for the threshold value, the focus detection can be executed withan even higher level of accuracy. It is to be noted that since the valuerepresenting the minimum correlation quantity C(x) is also dependent onthe number of sets of data used in the correlational arithmeticoperation, the value representing the minimum correlation quantity C(x)is first standardized based upon the number of sets of data used in thecorrelational arithmetic operation before the value is used in thejudging process. The focus detection is judged to be unreliable if theparameter SLOP expressed in (5) is equal to or less than a thresholdvalue. This threshold value is set to assume specific values so thatmore rigorous judging criteria are applied in the image sensor AF thanfor the exclusive AF. By selecting such values for the threshold value,the focus detection can be executed with an even higher level ofaccuracy. It is to be noted that since the value representing theparameter SLOP is also dependent on the number of sets of data used inthe correlational arithmetic operation, the value representing theparameter SLOP is first standardized based upon the number of sets ofdata used in the correlational arithmetic operation before the value isused in the judging process.

—Focus Match Verification Range—

The term “focus match verification range” refers to the defocus amountrange over which a focus matched state is recognized in step S150 andstep S210 in the flowchart presented in FIG. 12. A wider focus matchverification range is set for the exclusive AF so as to allow the lensto be driven quickly to a position near the focus match point and setthe imaging device in a shutter release ready state. However, a narrowerfocus match verification range is selected for the image sensor AF so asto achieve a highly accurate focus match during the imaging operation.

—Focus Match Area—

The term “focus match area” refers to the subject capturing areadetermined in step S140 in the flowchart presented in FIG. 12. The focusdetection is executed over a plurality of AF areas through the exclusiveAF better suited for simultaneous focus detection at multiple detectionpositions, at an early stage of the focus detection operation. Then, theplurality of defocus quantities obtained through the focus detectionthrough the exclusive AF are arithmetically processed by using aspecific algorithm to determine the AF area where the subject appears tobe captured. The image sensor AF is not suited to focus detectionexecuted simultaneously at a plurality of focus detection positions, isengaged to execute highly accurate focus detection in the AF area havingbeen selected through the exclusive AF.

—Offset Amount—

The term “offset amount” refers to the extent to which the calculateddefocus amount is fine-adjusted as has been explained in reference tostep S440 in FIG. 14. A defocus amount detected via the image sensor AFunit achieved by disposing focus detection pixels and imaging pixels ona single image sensor substrate directly corresponds to the state offocus adjustment in the image formed on the image sensor. Since theexclusive AF unit is built into the camera body as a unit independent ofthe image sensor, an offset amount needs to be incorporated into thedefocus amount detected through the exclusive AF in order to ultimatelyachieve a focus match on the image sensor.

It is to be noted that if different range-finding F values are assumedfor the image sensor AF and the exclusive AF, the focus match positionsdetermined through the image sensor AF and the exclusive AF may changedue to the optical characteristics (spherical aberration and the like)of the photographic optical system, which may ultimately alter theoffset amount. Under such circumstances, the offset amount should beadjusted based upon the optical characteristics data included in thelens information.

Likewise, if the minimum f-number of the exchangeable lens is a greaterthan the range-finding f-number assumed for the image sensor AF or theexclusive AF, an eclipse of the focus detection light fluxes may occurto change the focus match positions determined through the image sensorAF and the exclusive AF, which may ultimately alter the offset amount aswell. Under such circumstances, the offset amount should be adjustedbased upon the minimum f-number indicated in the lens information.

In addition, focus detection may be executed simultaneously by engagingthe exclusive AF unit and the image sensor AF unit for a givenphotographic subject on a regular basis, and the offset amount may beupdated by using the difference between the defocus quantities mostrecently calculated through the exclusive AF and the image sensor AF. Byupdating the offset amount in this manner, the focus detection can beexecuted with reliable accuracy even when the positions of the imagesensor AF unit and the exclusive AF unit change due to certainenvironmental conditions such as the humidity, the temperature and thelike or even when their positions change over time due to mechanicalwear and the like of movable members such as the sub mirror constitutingthe light flux switching means.

Table 5 indicates that different AF algorithm parameter settings areselected for the exclusive AF unit engaged during the early stage of thefocus adjustment operation and for the image sensor AF unit engagedduring the final stage of the focus adjustment operation, so as toachieve an optimal balance satisfying both the high responserequirements and the high accuracy requirements in the overall focusadjustment operation. Matching settings should be selected for theparameters in Table 5 if different focus detection positions are assumedfor the exclusive AF and the image sensor AF so that the focus detectionperformance does not greatly fluctuate no matter which focus detectionposition (AF area) is selected.

Further examples of variations are now explained. The half mirror shownin FIG. 1 or FIG. 18 may adopt a structure other than that achieved byforming a translucent film on a glass plate, as long as it constitutes alight splitting means for splitting light. For instance, it may beformed by bonding two triangular prism blocks at their inclined surfacesand forming a multi-layer film with a half mirror function at theattached surfaces. This structure effectively prevents reflection at therear surface, which tends to occur readily when a glass plate is usedand, as a result, the focus detection performance and the image qualityare both improved. Alternatively, the half mirror may be constitutedwith a pellicle mirror disposed over a thin film. This structure, too,effectively prevents reflection at the rear surface, which tends tooccur readily when a glass plate is used and, as a result, the focusdetection performance and the image quality are both improved.

Moreover, instead of a mirror that quantitatively splits light, aspectroscopic mirror that divides light according to wavelength may beused. For instance, a spectroscopic mirror that directs visible light tobe received at the image sensor AF unit and directs infrared light to bereceived at the exclusive AF unit may be utilized. In conjunction withsuch a mirror, a sufficient quantity of light to be used in the imagingoperation can be assured with ease. Alternatively, a polarizing halfmirror may be used in conjunction with a circular polarization filter atwhich incident light is received so as to selectively transmit orreflect part of the light having passed through the circularpolarization filter, which has been polarized along a specificdirection. The use of such a polarization half mirror prevents anywavelength-attributed fluctuation of the transmittance and thereflectance, which tends to occur readily when a half mirror constitutedwith a multilayer film is used.

The imaging and focus detection apparatus according to the presentinvention is not limited to a digital still camera constituted with anexchangeable lens and a camera body. The present invention may also beadopted in a digital still camera with an integrated lens or a videocamera. It may also be adopted in a compact camera module or the likebuilt into a device such as a portable telephone.

As explained above, the focus adjustment device in an embodimentcomprises an image sensor that includes imaging pixels for capturing animage formed via an imaging optical system and focus detection pixelsfor detecting a focus adjustment state at the imaging optical systemthrough a first pupil division-type image shift detection method, afocus detector that detects a focus adjustment state at the imagingoptical system through a second pupil division-type image shiftdetection method different from the first pupil division-type imageshift detection method, and a focus adjustment controller that executesfocus adjustment for the imaging optical system based upon the focusadjustment states detected by the image sensor and the focus detector.As a result, high response and highly accurate focal point adjustment isrealized.

The focus adjustment device in an embodiment comprises an image sensorthat includes imaging pixels for capturing an image formed via animaging optical system and focus detection pixels for detecting a focusadjustment state at the imaging optical system through a firstprocessing process, a focus detector that detects a focus adjustmentstate at the imaging optical system through a second processing processdifferent from the first processing process, and a focus adjustmentcontroller that executes focus adjustment for the imaging optical systembased upon the focus adjustment states detected by the image sensor andthe focus detector. As a result, high response and highly accurate focalpoint adjustment is realized.

In addition, since both the image sensor and the focus detector adoptthe pupil division-type focus detection method, no significantdiscrepancy occurs in the focus detection results and a smooth andnatural switch-over between the focus detection via the image sensor andthe focus detection via the focus detector is enabled. Since optimalstructures of the pupil division-type focus detection and optimalsettings for the various parameters of the pupil division-type focusdetection algorithm can be selected in correspondence to the conditionsunder which the individual focus detection functions are engaged,settings that will allow the individual focus detection functions tocomplement each other can be selected, and by switching to the specificfocus detection function to suit a specific set of conditions, the levelof overall focus detection performance can be improved.

The focus adjustment device in an embodiment includes an optical elementthat splits the light path of the imaging optical system into a pathextending toward the image sensor and a path extending toward the focusdetector or switches from one path to the other. Via this opticalelement, either the first pupil division-type image shift detectionmethod in the image sensor or the second pupil division-type image shiftdetection method in the focus detector can be selected to better suitthe specific set of conditions under which the focus detection isexecuted. In addition, since the focus detection is executed based upona single principle, no significant discrepancy occurs in the focusdetection results and a smooth and natural switch-over between the focusdetection via the image sensor and the focus detection via the focusdetector is enabled.

In the focus detection device in an embodiment, imaging pixels and focusdetection pixels are disposed on a single substrate, and the focusdetection pixels each include a micro-lens and a pair of photoelectricconversion units provided in correspondence to the micro-lens. The imagesensor, at which focus detection is executed by adopting the micro-lensmethod, can be provided as a compact unit. Furthermore, since the focusdetection can be ultimately executed on a plane which exactly matchesthe imaging plane, highly accurate focus detection can be achieved byeliminating an error in the alignment of the image sensor and the focusdetector and an error occurred with regard to the position of the imagesensor itself.

In an embodiment, the focus adjustment for the imaging optical system isexecuted by initially executing focus adjustment for the imaging opticalsystem based upon the detection results provided by the focus detectoruntil the photographing operation starts and then by executing focusadjustment for the imaging optical system based upon the detectionresults provided by the image sensor once the photographing operationstarts. This structure, which enables both high-response focusadjustment based upon the detection results provided by the focusdetector and highly accurate focus adjustment based upon the detectionresults provided by the image sensor, makes it possible to quickly andaccurately focus on a target subject.

The focus detection device in an embodiment comprises an image sensorthat includes imaging pixels for capturing an image formed via animaging optical system and focus detection pixels for detecting adefocus amount at the imaging optical system through a pupildivision-type method, a focus detector that detects a focus adjustmentstate at the imaging optical system through a pupil division-typemethod, a focus adjustment controller that executes focus adjustment forthe imaging optical system based upon the focus adjustment statesdetected by the image sensor and the focus detector, and a correctorthat corrects the defocus amount detected by the focus detector byadding an offset thereto so as to equalize the defocus amount with thedefocus amount detected by the image sensor. As a result, even if theimage sensor and the focus detector is switched based upon thephotographic condition and the like, the focus detection results are inagreement and a smooth and natural switch-over between the focusdetection via the image sensor and the focus detection via the focusdetector is enabled.

In the embodiment, the offset represents a difference between thedefocus amount detected by the image sensor and the defocus amountdetected by the focus detector in correspondence to a singlephotographic subject. As a result, the focus detection results betweenthe image sensor and the focus detector are in agreement and a smoothand natural switch-over between the focus detection via the image sensorand the focus detection via the focus detector is enabled.

In the embodiment, since the offset is set in correspondence to opticalcharacteristics of the imaging optical system, different focus statesbetween the image sensor and the focus detector are not detected indifferent optical characteristics of the imaging optical system.

The focus detection device in an embodiment further comprises a storagedevice that stores the offset, and the focus adjustment controllerupdates the offset based upon the defocus quantities detected by theimage sensor and the focus detector. As a result, the correct offset isobtained at all times.

1. An imaging device, comprising: a first image sensor that includesimaging pixels for capturing an image formed via an imaging opticalsystem and focus detection pixels for detecting a focus adjustment stateat the imaging optical system based upon a shift amount between a pairof images formed with light fluxes passing through a pair of areas on apupil of the imaging optical system; a focus detector that detects afocus adjustment state at the imaging optical system based upon a shiftamount between a pair of images formed with light fluxes passing througha pair of areas on a pupil of the imaging optical system; a focusadjustment controller that executes focus adjustment for the imagingoptical system based upon the focus adjustment state detected by thefirst image sensor or the focus detector selected in correspondence tophotographic conditions; and an optical element capable of directing alight flux from the imaging optical system along a light path extendingtoward the first image sensor and along a light path extending towardthe focus detector, wherein: the first image sensor includes the imagingpixels and the focus detection pixels disposed on a single substrate,the focus detector includes a pair of re-focusing lenses for reformingan image formed at a predetermined image plane of the imaging opticalsystem and a second image sensor that detects images reformed via thepair of re-focusing lenses, and the focus adjustment controller executesfocus adjustment for the imaging optical system based upon the focusadjustment state detected by the first image sensor while a movieshooting is in progress with the light flux from the imaging opticalsystem directed along the light path extending toward the first imagesensor.
 2. An imaging device according to claim 1, wherein: the focusdetection pixels each include a micro-lens and a pair of photoelectricconversion units provided in correspondence to the micro-lens.